diff --git a/src/engine/blocks.js b/src/engine/blocks.js
index b89a41b5d..f2d792d6b 100644
--- a/src/engine/blocks.js
+++ b/src/engine/blocks.js
@@ -487,6 +487,10 @@ class Blocks {
             }
             break;
         }
+
+        // forceNoGlow is set to true on containers that don't affect the project serialization,
+        // e.g., the toolbox or monitor containers.
+        if (optRuntime && !this.forceNoGlow) optRuntime.emitProjectChanged();
     }
 
     // ---------------------------------------------------------------------
diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index e16ac5411..fa9c366bd 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -501,6 +501,14 @@ class Runtime extends EventEmitter {
         return 'PROJECT_LOADED';
     }
 
+    /**
+     * Event name for report that a change was made that can be saved
+     * @const {string}
+     */
+    static get PROJECT_CHANGED () {
+        return 'PROJECT_CHANGED';
+    }
+
     /**
      * Event name for targets update report.
      * @const {string}
@@ -1737,7 +1745,6 @@ class Runtime extends EventEmitter {
         // Script glows must be cleared.
         this._scriptGlowsPreviousFrame = [];
         this._updateGlows();
-        this.requestTargetsUpdate(editingTarget);
     }
 
     /**
@@ -2035,6 +2042,13 @@ class Runtime extends EventEmitter {
         this.emit(Runtime.PROJECT_LOADED);
     }
 
+    /**
+     * Report that the project has changed in a way that would affect serialization
+     */
+    emitProjectChanged () {
+        this.emit(Runtime.PROJECT_CHANGED);
+    }
+
     /**
      * Report that a new target has been created, possibly by cloning an existing target.
      * @param {Target} newTarget - the newly created target.
diff --git a/src/virtual-machine.js b/src/virtual-machine.js
index 6f15c43d1..b829664a2 100644
--- a/src/virtual-machine.js
+++ b/src/virtual-machine.js
@@ -84,6 +84,9 @@ class VirtualMachine extends EventEmitter {
         this.runtime.on(Runtime.PROJECT_RUN_STOP, () => {
             this.emit(Runtime.PROJECT_RUN_STOP);
         });
+        this.runtime.on(Runtime.PROJECT_CHANGED, () => {
+            this.emit(Runtime.PROJECT_CHANGED);
+        });
         this.runtime.on(Runtime.VISUAL_REPORT, visualReport => {
             this.emit(Runtime.VISUAL_REPORT, visualReport);
         });
@@ -476,7 +479,7 @@ class VirtualMachine extends EventEmitter {
             }
 
             // Update the VM user's knowledge of targets and blocks on the workspace.
-            this.emitTargetsUpdate();
+            this.emitTargetsUpdate(false /* Don't emit project change */);
             this.emitWorkspaceUpdate();
             this.runtime.setEditingTarget(this.editingTarget);
             this.runtime.ioDevices.cloud.setStage(this.runtime.getTargetForStage());
@@ -1105,7 +1108,7 @@ class VirtualMachine extends EventEmitter {
         if (target) {
             this.editingTarget = target;
             // Emit appropriate UI updates.
-            this.emitTargetsUpdate();
+            this.emitTargetsUpdate(false /* Don't emit project change */);
             this.emitWorkspaceUpdate();
             this.runtime.setEditingTarget(target);
         }
@@ -1199,6 +1202,7 @@ class VirtualMachine extends EventEmitter {
         if (this.editingTarget) {
             this.emitWorkspaceUpdate();
             this.runtime.setEditingTarget(this.editingTarget);
+            this.emitTargetsUpdate(false /* Don't emit project change */);
         }
     }
 
@@ -1206,8 +1210,12 @@ class VirtualMachine extends EventEmitter {
      * Emit metadata about available targets.
      * An editor UI could use this to display a list of targets and show
      * the currently editing one.
+     * @param {bool} triggerProjectChange If true, also emit a project changed event.
+     * Disabled selectively by updates that don't affect project serialization.
+     * Defaults to true.
      */
-    emitTargetsUpdate () {
+    emitTargetsUpdate (triggerProjectChange) {
+        if (typeof triggerProjectChange === 'undefined') triggerProjectChange = true;
         this.emit('targetsUpdate', {
             // [[target id, human readable target name], ...].
             targetList: this.runtime.targets
@@ -1220,6 +1228,7 @@ class VirtualMachine extends EventEmitter {
             // Currently editing target id.
             editingTarget: this.editingTarget ? this.editingTarget.id : null
         });
+        if (triggerProjectChange) this.runtime.emitProjectChanged();
     }
 
     /**