Remove item from subgroups in Group remove method

lib/timeline/component/Group.js

@@ -388,7 +388,13 @@ Group.prototype.remove = function(item) {
   var index = this.visibleItems.indexOf(item);
   if (index != -1) this.visibleItems.splice(index, 1);
 
-  // TODO: also remove from ordered items?
+  if(item.data.subgroup !== undefined){
+    var subgroup = this.subgroups[item.data.subgroup];
+    if(subgroup){
+      var itemIndex = subgroup.items.indexOf(item);
+      subgroup.items.splice(itemIndex,1);
+    }
+  }
 };