diff --git a/core/block_events.js b/core/block_events.js
index 8638a57e0..7c80dfca7 100644
--- a/core/block_events.js
+++ b/core/block_events.js
@@ -177,16 +177,16 @@ Blockly.Events.Change.prototype.run = function(forward) {
       }
       break;
     case 'comment':
-      block.setCommentText(value || null);
+      block.setCommentText(/** @type {string} */ (value) || null);
       break;
     case 'collapsed':
-      block.setCollapsed(value);
+      block.setCollapsed(!!value);
       break;
     case 'disabled':
       block.setEnabled(!value);
       break;
     case 'inline':
-      block.setInputsInline(value);
+      block.setInputsInline(!!value);
       break;
     case 'mutation':
       var oldMutation = '';
@@ -195,7 +195,7 @@ Blockly.Events.Change.prototype.run = function(forward) {
         oldMutation = oldMutationDom && Blockly.Xml.domToText(oldMutationDom);
       }
       if (block.domToMutation) {
-        var dom = Blockly.Xml.textToDom(value || '<mutation/>');
+        var dom = Blockly.Xml.textToDom(/** @type {string} */ (value) || '<mutation/>');
         block.domToMutation(dom);
       }
       Blockly.Events.fire(new Blockly.Events.Change(
@@ -223,7 +223,7 @@ Blockly.Events.Create = function(block) {
   } else {
     this.xml = Blockly.Xml.blockToDom(block);
   }
-  this.ids = Blockly.Events.getDescendantIds_(block);
+  this.ids = Blockly.Events.getDescendantIds(block);
 };
 Blockly.utils.object.inherits(Blockly.Events.Create, Blockly.Events.BlockBase);
 
@@ -276,7 +276,7 @@ Blockly.Events.Create.prototype.run = function(forward) {
     for (var i = 0, id; id = this.ids[i]; i++) {
       var block = workspace.getBlockById(id);
       if (block) {
-        block.dispose(false, false);
+        block.dispose(false);
       } else if (id == this.blockId) {
         // Only complain about root-level block.
         console.warn("Can't uncreate non-existent block: " + id);
@@ -305,7 +305,7 @@ Blockly.Events.Delete = function(block) {
   } else {
     this.oldXml = Blockly.Xml.blockToDom(block);
   }
-  this.ids = Blockly.Events.getDescendantIds_(block);
+  this.ids = Blockly.Events.getDescendantIds(block);
 };
 Blockly.utils.object.inherits(Blockly.Events.Delete, Blockly.Events.BlockBase);
 
@@ -352,7 +352,7 @@ Blockly.Events.Delete.prototype.run = function(forward) {
     for (var i = 0, id; id = this.ids[i]; i++) {
       var block = workspace.getBlockById(id);
       if (block) {
-        block.dispose(false, false);
+        block.dispose(false);
       } else if (id == this.blockId) {
         // Only complain about root-level block.
         console.warn("Can't delete non-existent block: " + id);
@@ -448,7 +448,7 @@ Blockly.Events.Move.prototype.recordNew = function() {
  * @private
  */
 Blockly.Events.Move.prototype.currentLocation_ = function() {
-  var workspace = Blockly.Workspace.getById(this.workspaceId);
+  var workspace = this.getEventWorkspace_();
   var block = workspace.getBlockById(this.blockId);
   var location = {};
   var parent = block.getParent();
diff --git a/core/events.js b/core/events.js
index bcc5cb100..a693cae04 100644
--- a/core/events.js
+++ b/core/events.js
@@ -195,6 +195,9 @@ Blockly.Events.fireNow_ = function() {
   var queue = Blockly.Events.filter(Blockly.Events.FIRE_QUEUE_, true);
   Blockly.Events.FIRE_QUEUE_.length = 0;
   for (var i = 0, event; event = queue[i]; i++) {
+    if (!event.workspaceId) {
+      continue;
+    }
     var workspace = Blockly.Workspace.getById(event.workspaceId);
     if (workspace) {
       workspace.fireChangeListener(event);
@@ -330,9 +333,9 @@ Blockly.Events.setGroup = function(state) {
  * Compute a list of the IDs of the specified block and all its descendants.
  * @param {!Blockly.Block} block The root block.
  * @return {!Array.<string>} List of block IDs.
- * @private
+ * @package
  */
-Blockly.Events.getDescendantIds_ = function(block) {
+Blockly.Events.getDescendantIds = function(block) {
   var ids = [];
   var descendants = block.getDescendants(false);
   for (var i = 0, descendant; descendant = descendants[i]; i++) {
@@ -373,13 +376,13 @@ Blockly.Events.fromJson = function(json, workspace) {
       event = new Blockly.Events.VarRename(null, '');
       break;
     case Blockly.Events.UI:
-      event = new Blockly.Events.Ui(null);
+      event = new Blockly.Events.Ui(null, '', '', '');
       break;
     case Blockly.Events.COMMENT_CREATE:
       event = new Blockly.Events.CommentCreate(null);
       break;
     case Blockly.Events.COMMENT_CHANGE:
-      event = new Blockly.Events.CommentChange(null);
+      event = new Blockly.Events.CommentChange(null, '', '');
       break;
     case Blockly.Events.COMMENT_MOVE:
       event = new Blockly.Events.CommentMove(null);
@@ -405,6 +408,9 @@ Blockly.Events.fromJson = function(json, workspace) {
 Blockly.Events.disableOrphans = function(event) {
   if (event.type == Blockly.Events.MOVE ||
       event.type == Blockly.Events.CREATE) {
+    if (!event.workspaceId) {
+      return;
+    }
     var workspace = Blockly.Workspace.getById(event.workspaceId);
     var block = workspace.getBlockById(event.blockId);
     if (block) {
diff --git a/core/events_abstract.js b/core/events_abstract.js
index 5f9073d30..99b8e6982 100644
--- a/core/events_abstract.js
+++ b/core/events_abstract.js
@@ -44,7 +44,7 @@ Blockly.Events.Abstract = function() {
    * perspective, and should be undone together.
    * @type {string}
    */
-  this.group = Blockly.Events.group_;
+  this.group = Blockly.Events.getGroup();
 
   /**
    * Sets whether the event should be added to the undo stack.
@@ -93,12 +93,14 @@ Blockly.Events.Abstract.prototype.run = function(_forward) {
 
 /**
  * Get workspace the event belongs to.
- * @return {Blockly.Workspace} The workspace the event belongs to.
+ * @return {!Blockly.Workspace} The workspace the event belongs to.
  * @throws {Error} if workspace is null.
  * @protected
  */
 Blockly.Events.Abstract.prototype.getEventWorkspace_ = function() {
-  var workspace = Blockly.Workspace.getById(this.workspaceId);
+  if (this.workspaceId) {
+    var workspace = Blockly.Workspace.getById(this.workspaceId);
+  }
   if (!workspace) {
     throw Error('Workspace is null. Event must have been generated from real' +
         ' Blockly events.');
diff --git a/core/inject.js b/core/inject.js
index 6cd73c6b0..74c755fa2 100644
--- a/core/inject.js
+++ b/core/inject.js
@@ -365,7 +365,9 @@ Blockly.createMainWorkspace_ = function(svg, options, blockDragSurface,
               console.log('WARNING: Moved object in bounds but there was no' +
                   ' event group. This may break undo.');
             }
-            Blockly.Events.setGroup(oldGroup);
+            if (oldGroup !== null) {
+              Blockly.Events.setGroup(oldGroup);
+            }
           }
         }
       }
diff --git a/core/ui_events.js b/core/ui_events.js
index 080ec3fc4..cc8cabcfb 100644
--- a/core/ui_events.js
+++ b/core/ui_events.js
@@ -44,7 +44,7 @@ goog.require('Blockly.utils.object');
 Blockly.Events.Ui = function(block, element, oldValue, newValue) {
   Blockly.Events.Ui.superClass_.constructor.call(this);
   this.blockId = block ? block.id : null;
-  this.workspaceId = block ? block.workspace.id : null;
+  this.workspaceId = block ? block.workspace.id : undefined;
   this.element = element;
   this.oldValue = oldValue;
   this.newValue = newValue;
diff --git a/core/workspace_events.js b/core/workspace_events.js
index 44b3a6af3..581366574 100644
--- a/core/workspace_events.js
+++ b/core/workspace_events.js
@@ -51,7 +51,7 @@ Blockly.Events.FinishedLoading = function(workspace) {
    * perspective, and should be undone together.
    * @type {string}
    */
-  this.group = Blockly.Events.group_;
+  this.group = Blockly.Events.getGroup();
 
   // Workspace events do not undo or redo.
   this.recordUndo = false;
diff --git a/core/ws_comment_events.js b/core/ws_comment_events.js
index be90436ff..7e62d5451 100644
--- a/core/ws_comment_events.js
+++ b/core/ws_comment_events.js
@@ -62,7 +62,7 @@ Blockly.Events.CommentBase = function(comment) {
    * perspective, and should be undone together.
    * @type {string}
    */
-  this.group = Blockly.Events.group_;
+  this.group = Blockly.Events.getGroup();
 
   /**
    * Sets whether the event should be added to the undo stack.
@@ -315,7 +315,7 @@ Blockly.Events.CommentMove = function(comment) {
 
   /**
    * The location after the move, in workspace coordinates.
-   * @type {!Blockly.utils.Coordinate}
+   * @type {Blockly.utils.Coordinate}
    */
   this.newCoordinate_ = null;
 };