diff --git a/node_modules/ace/lib/ace/edit_session.js b/node_modules/ace/lib/ace/edit_session.js
index cfd7b174..e385647a 100644
--- a/node_modules/ace/lib/ace/edit_session.js
+++ b/node_modules/ace/lib/ace/edit_session.js
@@ -260,10 +260,10 @@ var EditSession = function(text, mode) {
                 this.$undoManager.add({
                     action: "removeFolds",
                     folds:  removedFolds
-                }, this);
+                }, this.mergeUndoDeltas);
                 this.mergeUndoDeltas = true;
             }
-            this.$undoManager.add(delta, this);
+            this.$undoManager.add(delta, this.mergeUndoDeltas);
             this.mergeUndoDeltas = true;
             
             this.$informUndoManager.schedule();
@@ -376,7 +376,7 @@ var EditSession = function(text, mode) {
         
         if (undoManager) {
             var self = this;
-            undoManager.$session = this;
+            undoManager.setSession(this);
             this.$syncInformUndoManager = function() {
                 self.$informUndoManager.cancel();
                 self.mergeUndoDeltas = false;
@@ -402,6 +402,7 @@ var EditSession = function(text, mode) {
         add: function() {},
         addSelection: function() {},
         startNewGroup: function() {},
+        setSession: function() {},
     };
 
     /**
diff --git a/node_modules/ace/lib/ace/undomanager.js b/node_modules/ace/lib/ace/undomanager.js
index b2ae7a8d..cd0f1711 100644
--- a/node_modules/ace/lib/ace/undomanager.js
+++ b/node_modules/ace/lib/ace/undomanager.js
@@ -44,11 +44,15 @@ define(function(require, exports, module) {
 var UndoManager = function() {
     this.$maxRev = 0;
     this.mark = 0;
+    this.$fromUndo = false;
     this.reset();
 };
 
 (function() {
-
+    
+    this.setSession = function(session) {
+        this.$session = session;
+    };
     /**
      * Provides a means for implementing your own undo manager. `options` has one property, `args`, an [[Array `Array`]], with two elements:
      *
@@ -58,8 +62,9 @@ var UndoManager = function() {
      * @param {Object} options Contains additional properties
      *
      **/
-    this.add = function(delta) {
-        if (this.$session.mergeUndoDeltas === false || !this.lastDeltas) {
+    this.add = function(delta, allowMerge) {
+        if (this.$fromUndo) return;
+        if (allowMerge === false || !this.lastDeltas) {
             this.lastDeltas = [];
             this.$undoStack.push(this.lastDeltas);
             delta.id = this.$rev = ++this.$maxRev;
@@ -84,10 +89,10 @@ var UndoManager = function() {
         var stack = this.$undoStack;
         for (var i = stack.length; i--;) {
             var delta = stack[i][0];
-            if (delta.id < to)
-                delta.ignore = true;
             if (delta.id <= from)
                 break;
+            if (delta.id < to)
+                delta.ignore = true;
         }
         this.lastDeltas = null;
     };
@@ -125,10 +130,12 @@ var UndoManager = function() {
     };
     
     this.getChangedRanges = function(from, to) {
+        if (to == null) to = this.$rev + 1;
         
     };
     
     this.getChangedLines = function(from, to) {
+        if (to == null) to = this.$rev + 1;
         
     };
     
@@ -141,18 +148,24 @@ var UndoManager = function() {
     this.undo = function(dontSelect) {
         this.lastDeltas = null;
         var stack = this.$undoStack;
-        findDelta(stack, stack.length);
+        
+        if (!rearrangeUndoStack(stack, stack.length))
+            return;
+        
+        if (this.$redoStackBaseRev !== this.$rev && this.$redoStack.length)
+            this.$redoStack = [];
+        
+        this.$fromUndo = true;
+        
         var deltaSet = stack.pop();
         var undoSelectionRange = null;
         if (deltaSet && deltaSet.length) {
-            var id = deltaSet[0].id;
             undoSelectionRange = this.$session.undoChanges(deltaSet, dontSelect);
-            if (this.$redoStackBaseRev !== id) {
-                this.$redoStack = [];
-            }
             this.$redoStack.push(deltaSet);
             this.$syncRev();
         }
+        
+        this.$fromUndo = false;
 
         return undoSelectionRange;
     };
@@ -164,6 +177,8 @@ var UndoManager = function() {
      **/
     this.redo = function(dontSelect) {
         this.lastDeltas = null;
+        
+        this.$fromUndo = true;
         if (this.$redoStackBaseRev != this.$rev) {
             var diff = this.getDeltas(this.$redoStackBaseRev, this.$rev + 1);
             rebaseRedoStack(this.$redoStack, diff);
@@ -180,13 +195,15 @@ var UndoManager = function() {
             this.$undoStack.push(deltaSet);
             this.$syncRev();
         }
+        this.$fromUndo = false;
+        
         return redoSelectionRange;
     };
     
     this.$syncRev = function() {
         var stack = this.$undoStack;
         var nextDelta = stack[stack.length - 1];
-        var id = nextDelta && nextDelta[0].id || 0;
+        var id = nextDelta && nextDelta[0] && nextDelta[0].id || 0;
         this.$redoStackBaseRev = id;
         this.$rev = id;
     };
@@ -202,11 +219,12 @@ var UndoManager = function() {
         this.selections = [];
     };
 
+    
     /**
      * Returns `true` if there are undo operations left to perform.
      * @returns {Boolean}
      **/
-    this.hasUndo = function() {
+    this.canUndo = function() {
         return this.$undoStack.length > 0;
     };
 
@@ -214,15 +232,14 @@ var UndoManager = function() {
      * Returns `true` if there are redo operations left to perform.
      * @returns {Boolean}
      **/
-    this.hasRedo = function() {
+    this.canRedo = function() {
         return this.$redoStack.length > 0;
     };
-
+    
     /**
      * Marks the current status clean
      **/
-    this.bookmark =
-    this.markClean = function(rev) {
+    this.bookmark = function(rev) {
         if (rev == undefined)
             rev = this.$rev;
         this.mark = rev;
@@ -232,14 +249,26 @@ var UndoManager = function() {
      * Returns if the current status is clean
      * @returns {Boolean}
      **/
-    this.isClean = function() {
+    this.isAtBookmark = function() {
         return this.$rev === this.mark;
     };
     
-
+    this.toJSON = function() {
+        
+    };
+    
+    this.fromJSON = function() {
+        
+    };
+    
+    this.hasUndo = this.canUndo;
+    this.hasRedo = this.canRedo;
+    this.isClean = this.isAtBookmark;
+    this.markClean = this.bookmark;
+    
 }).call(UndoManager.prototype);
 
-function findDelta(stack, pos) {
+function rearrangeUndoStack(stack, pos) {
     for (var i = pos; i--; ) {
         var deltaSet = stack[i];
         if (deltaSet && !deltaSet[0].ignore) {
@@ -249,7 +278,7 @@ function findDelta(stack, pos) {
                 stack[i + 1] = swapped[1];
                 i++;
             }
-            break;
+            return true;
         }
     }
 }
diff --git a/plugins/c9.ide.ace/ace.js b/plugins/c9.ide.ace/ace.js
index c7e35fd7..3f6bca39 100644
--- a/plugins/c9.ide.ace/ace.js
+++ b/plugins/c9.ide.ace/ace.js
@@ -282,14 +282,24 @@ define(function(require, exports, module) {
         /***** Undo Manager *****/
         
         function AceUndoManager(undoManager, session) {
+            var state = undoManager.getState();
             this.$session = session;
             this.$undo = undoManager;
             this.$aceUndo = new UndoManager();
-            var _self = this;
-            var Item = this.Item;
-            this.$undo.on("itemFind", function(e) {
-                return Item(_self, e.state);
-            });
+            this.$aceUndo.c9UndoProxy = undoManager;
+            undoManager.$aceUndo = this.$aceUndo;
+            undoManager.add = this.add;
+            undoManager.addSelection = this.addSelection;
+            undoManager.undo = this.undo;
+            undoManager.redo = this.redo;
+            undoManager.reset = this.reset;
+            undoManager.canUndo = this.canUndo;
+            undoManager.canRedo = this.canRedo;
+            undoManager.getState = this.getState;
+            undoManager.setState = this.setState;
+            this._emit = undoManager.getEmitter();
+            
+            undoManager.setState(state);
         }
         function updateDeltas(deltas) {
             if (deltas[0] && deltas[0].deltas) {
@@ -299,81 +309,74 @@ define(function(require, exports, module) {
                     deltas.push.apply(deltas, x.deltas);
                 });
             }
+            return deltas;
         }
         AceUndoManager.prototype = {
-            rebase: function() {
-                var pos = this.$undo.position + 2;
-                var stack = this.$undo.stack;
-                for (var i = pos; i--; ) {
-                    var deltaSet = stack[i].deltas;
-                    if (deltaSet[0] && !deltaSet[0].disabled) {
-                        while(i < pos - 1) {
-                            var swapped = UndoManager.swapGroups(stack[i].deltas, stack[i + 1].deltas);
-                            stack[i].deltas = swapped[0];
-                            stack[i + 1].deltas = swapped[1];
-                            i++;
-                        }
-                        deltaSet = stack[pos - 1].deltas;
-                        if (deltaSet[0].disabled)
-                            deltaSet[0].disabled = false;
-                        return deltaSet;
-                    }
-                }
-            },
-            Item: function(_self, deltas) {
-                return {
-                    deltas: deltas,
-                    undo: function(){
-                        updateDeltas(this.deltas); // change to the new format
-                        var deltas = _self.rebase();
-                        if (!deltas)
-                            return false;
-                        _self.$session.session.undoChanges(deltas, _self.dontSelect);
-                    },
-                    redo: function(){
-                        updateDeltas(this.deltas);
-                        _self.$session.session.redoChanges(this.deltas, _self.dontSelect);
-                    },
-                    getState: function(){
-                        updateDeltas(this.deltas);
-                        return this.deltas.filter(function (d) {
-                            return d.action == "insert" || d.action == "remove";
-                        });
-                    }
-                };
-            },
-            
             add: function(delta, doc) {
-                if (doc.mergeUndoDeltas === false || !this.lastDeltas) {
-                    this.lastDeltas = [];
-                    this.$undo.add(this.Item(this, this.lastDeltas));
-                }
-                this.lastDeltas.push(delta);
+                this.$aceUndo.add(delta, doc);
+                this._emit("change");
+            },
+            addSelection: function(range, rev) {
+                this.$aceUndo.addSelection(range, rev);
             },
-
             undo: function(dontSelect) {
-                this.dontSelect = dontSelect;
-                this.lastDeltas = null;
-                this.$undo.undo();
+                this.$aceUndo.undo(dontSelect);
+                this._emit("change");
             },
             redo: function(dontSelect) {
-                this.dontSelect = dontSelect;
-                this.lastDeltas = null;
-                this.$undo.redo();
+                this.$aceUndo.redo(dontSelect);
+                this._emit("change");
             },
             reset: function(){
-                this.lastDeltas = null;
-                this.$undo.reset();
+                this.$aceUndo.reset();
+                this._emit("change");
             },
-            hasUndo: function() {
-                return this.$undo.length > this.$undo.position + 1;
+            canUndo: function() {
+                return this.$aceUndo.canUndo();
             },
-            hasRedo: function() {
-                return this.$undo.length <= this.$undo.position + 1;
+            canRedo: function() {
+                return this.$aceUndo.canRedo();
             },
-            get $undoStack() {
-                return this.$undo.stack.slice(0, this.$undo.position + 1)
-                    .map(function(e){ return e.getState ? e.getState() : e });
+            clearUndo: function() {
+                this.$aceUndo.$undoStack = [];
+                this._emit("change");
+            },
+            clearRedo: function() {
+                this.$aceUndo.$redoStack = [];
+                this._emit("change");
+            },
+            getState: function() {
+                console.log("getState()");
+                var aceUndo = this.$aceUndo;
+                var stack = aceUndo.$undoStack.map(function(deltaSet) {
+                    return deltaSet.filter(function (d) {
+                        return d.action == "insert" || d.action == "remove";
+                    });
+                });
+                return {
+                    stack: stack,
+                    mark: aceUndo.mark,
+                    position: aceUndo.$rev
+                };
+            },
+            setState: function(e) {
+                console.log("setState()");
+                var aceUndo = this.$aceUndo;
+                aceUndo.$undoStack = (e.stack || []).filter(function(x) {
+                    return x.length;
+                });
+                aceUndo.$rev = e.position;
+                this.bookmark(e.mark);
+            },
+            isAtBookmark: function() {
+                return this.$aceUndo.isAtBookmark();
+            },
+            bookmark: function(index) {
+                this.$aceUndo.bookmark(index);
+                this._emit("change");
+            },
+            setSession: function(session) {
+                this.$aceUndo.setSession(session);
             }
         };
         
@@ -383,9 +386,19 @@ define(function(require, exports, module) {
         }
         
         (function() {
-            this.execute = function(options) {
-                this.$u.execute(options);
+            this.add = function(delta, doc) {
+                this.$u.add(delta, doc);
             };
+            
+            Object.defineProperty(this, "", {
+                configurable: true,
+                get: function() {
+                    return this.$u.lastDeltas;
+                },
+                set: function(v) {
+                    this.$u.lastDeltas = v;
+                }
+            });
         
             this.undo = function() {
                 var selectionRange = this.$u.undo(true);
@@ -1410,7 +1423,7 @@ define(function(require, exports, module) {
                 undoManager = session.getUndoManager();
             if (undoManager) {
                 var undoManagerProxy = new UndoManagerProxy(undoManager, s);
-                s.setUndoManager(undoManagerProxy);
+                s.setUndoManager(undoManagerProxy.$aceUndo);
             }
     
             // Overwrite the default $informUndoManager function such that new deltas
@@ -2211,9 +2224,9 @@ define(function(require, exports, module) {
                 var c9Session = doc.getSession();
                 
                 // if load starts from another editor type
-                // tabmanager will show as instantly
+                // tabmanager will show us instantly
                 // so we need to show progress bar instantly
-                progress.noFadeIn = !currentDocument;
+                progress.noFadeIn = !currentDocument || !currentDocument.tab.active;
                 
                 // Value Retrieval
                 doc.on("getValue", function get(e) {
diff --git a/plugins/c9.ide.editors/undomanager.js b/plugins/c9.ide.editors/undomanager.js
index 6560de05..db1e90a0 100644
--- a/plugins/c9.ide.editors/undomanager.js
+++ b/plugins/c9.ide.editors/undomanager.js
@@ -150,6 +150,8 @@ define(function(require, module, exports) {
                 emit("change");
             }
             
+            plugin.freezePublicAPI.baseclass();
+            
             /**
              * The Undo Manager class of Cloud9. Each {@link Document} 
              * has a single instance of the undo manager that
@@ -212,10 +214,6 @@ define(function(require, module, exports) {
              * 
              **/
             plugin.freezePublicAPI({
-                /**
-                 * @ignore
-                 */
-                get stack() { return stack; },
                 /**
                  * The number of items on the stack. This number will stay the
                  * same when using {@link UndoManager#undo} and