diff --git a/HISTORY.md b/HISTORY.md
index 446aa31f..cf31750f 100755
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -49,6 +49,9 @@
 * **Translation Updates:**
     * German
 
+### 2022-05-25
+* threads: update programmatic custom block-type changes in data references
+
 ### 2022-05-23
 * blocks: fixed block label color when expanding or inserting variadic infix slots 
 
diff --git a/snap.html b/snap.html
index 14afaf8b..15b12113 100755
--- a/snap.html
+++ b/snap.html
@@ -17,7 +17,7 @@
         <script src="src/symbols.js?version=2021-03-03"></script>
         <script src="src/widgets.js?version=2021-17-09"></script>
         <script src="src/blocks.js?version=2022-05-23"></script>
-        <script src="src/threads.js?version=2022-05-20"></script>
+        <script src="src/threads.js?version=2022-05-25"></script>
         <script src="src/objects.js?version=2022-05-20"></script>
         <script src="src/scenes.js?version=2022-03-03"></script>
         <script src="src/gui.js?version=2022-05-19"></script>
diff --git a/src/threads.js b/src/threads.js
index 5a3e073a..2e642b3d 100644
--- a/src/threads.js
+++ b/src/threads.js
@@ -65,7 +65,7 @@ StagePickerMorph, CustomBlockDefinition*/
 
 /*jshint esversion: 11, bitwise: false, evil: true*/
 
-modules.threads = '2022-May-20';
+modules.threads = '2022-May-25';
 
 var ThreadManager;
 var Process;
@@ -5640,6 +5640,7 @@ Process.prototype.doSetBlockAttribute = function (attribute, block, val) {
         expr,
         def,
         template,
+        oldType,
         type;
 
     this.assertType(block, types);
@@ -5666,6 +5667,12 @@ Process.prototype.doSetBlockAttribute = function (attribute, block, val) {
         }
     }
 
+    function isMajorTypeChange() {
+        var rep = ['reporter', 'predicate'];
+        return (type === 'command' && rep.includes(oldType)) ||
+            (oldType == 'command' && rep.includes(type));
+    }
+
     switch (choice) {
     case 'label':
         def.setBlockLabel(val);
@@ -5698,10 +5705,27 @@ Process.prototype.doSetBlockAttribute = function (attribute, block, val) {
         if (rcvr.allBlockInstances(def).every(block =>
             block.isChangeableTo(type))
         ) {
+            oldType = def.type;
             def.type = type;
         } else {
             throw new Error('cannot change this\nfor a block that is in use');
         }
+        if (isMajorTypeChange()) {
+            // since we've already scanned all contexts we know that those
+            // that contain block instances only contain single, unattached
+            // ones. Therefore we can simply replace them with new ones.
+            if (def.isGlobal) {
+                ide.stage.allContextsUsing(def).forEach(context =>
+                    context.expression = def.blockInstance()
+                );
+            } else {
+                ide.stage.allContextsInvoking(def.blockSpec(), rcvr).forEach(
+                    context => context.expression = def.blockInstance()
+                );
+            }
+        }
+
+
         break;
     case 'scope':
         if (isInUse()) {