Index: /CKEditor/trunk/_source/plugins/dialog/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/dialog/plugin.js	(revision 3251)
+++ /CKEditor/trunk/_source/plugins/dialog/plugin.js	(revision 3252)
@@ -1028,5 +1028,8 @@
 			add : function( name, dialogDefinition )
 			{
-				this._.dialogDefinitions[name] = dialogDefinition;
+				// Avoid path registration from multiple instances override definition.
+				if ( !this._.dialogDefinitions[name] 
+					|| typeof  dialogDefinition == 'function' )
+					this._.dialogDefinitions[name] = dialogDefinition;
 			},