Confine programmatically setting the “temporary?” attribute to dev mode

because it has serious pitfall issues

blocks.js

@@ -148,7 +148,7 @@ CustomCommandBlockMorph, SymbolMorph*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.blocks = '2017-August-29';
+modules.blocks = '2017-August-30';
 
 var SyntaxElementMorph;
 var BlockMorph;
@@ -8289,7 +8289,9 @@ InputSlotMorph.prototype.gettablesMenu = function () {
     if (StageMorph.prototype.enableInheritance) {
         dict.children = ['children'];
         dict.parent = ['parent'];
-        dict['temporary?'] = ['temporary?'];
+        if (this.world().isDevMode) {
+            dict['temporary?'] = ['temporary?'];
+        }
     }
     dict.name = ['name'];
     dict.costumes = ['costumes'];

history.txt

@@ -3594,6 +3594,10 @@ Fixes:
 * GUI, Objects: enable exporting costumes and variable-data in the newest Chrome version, which disables opening tabs on dataURLs
 * Blocks, Threads: added “temporary?” as gettable and settable attribute for clones
 
+170830
+------
+* Blocks, Threads: Confine programmatically setting the “temporary?” attribute to dev mode
+
 
 Features:
 * polymorphic sprite-local custom blocks

threads.js

@@ -61,7 +61,7 @@ StageMorph, SpriteMorph, StagePrompterMorph, Note, modules, isString, copy,
 isNil, WatcherMorph, List, ListWatcherMorph, alert, console, TableMorph,
 TableFrameMorph, ColorSlotMorph, isSnapObject*/
 
-modules.threads = '2017-August-29';
+modules.threads = '2017-August-30';
 
 var ThreadManager;
 var Process;
@@ -3195,12 +3195,13 @@ Process.prototype.doSet = function (attribute, value) {
     case 'temporary?':
         this.assertType(rcvr, 'sprite');
         this.assertType(value, 'Boolean');
-        if (value) {
-            rcvr.release();
-        } else {
-            rcvr.perpetuate();
+        if (rcvr.world().isDevMode) {
+            if (value) {
+                rcvr.release();
+            } else {
+                rcvr.perpetuate();
+            }
         }
-        rcvr.version = Date.now();
         break;
     case 'dangling?':
         this.assertType(rcvr, 'sprite');