disabled "when this scene starts" hat blocks to directly switch to another scene

HISTORY.md

@@ -37,6 +37,7 @@
 * objects: changed category for "switch to scene" to control
 * blocks, objects, threads: new hat block for "when this scene starts"
 * blocks, threads: changed "switch to scene" to be a stop block
+* threads: disabled "when this scene starts" hat blocks to directly switch to another scene
 
 ### 2021-09-07
 * blocks, objects, threads: new change-of-scene event

src/threads.js

@@ -4710,7 +4710,12 @@ Process.prototype.doSwitchToScene = function (id) {
         ide, scenes, num, scene;
 
     this.assertAlive(rcvr);
-    if (this.readyToTerminate) {return; } // let the user press "stop" or "esc"
+    if (this.readyToTerminate || this.topBlock.selector === 'receiveOnScene') {
+        // let the user press "stop" or "esc",
+        // prevent "when this scene starts" hat blocks from directly
+        // switching to another
+        return;
+    }
     ide = rcvr.parentThatIsA(IDE_Morph);
     scenes = ide.scenes;