This patch simply removes a warning when the debug tracing is enabled.

Index: frontend/framework/source/class/qx/ui/form/ComboBoxEx.js
===================================================================
--- frontend/framework/source/class/qx/ui/form/ComboBoxEx.js	(revision 8461)
+++ frontend/framework/source/class/qx/ui/form/ComboBoxEx.js	(working copy)
@@ -1622,6 +1622,7 @@
       this._popup.setParent(null);
     }
 
+    this._disposeFields("_data");
     this._disposeObjects("_popup", "_list", "_manager", "_field", "_button");
   }
 });