As the summary, says JSEventTargetNode::getListener function blindly casts an EventListener object to a JSEventListener. This will fail if ie. it's actually an ObjCEventListener.
The getListener/setListener functions of the JSEventTarget* classes are only used when calling someElement.onclick = '...' or someElement.onclick.handleEvent(..). The official DOM methods are not affected.
A test case would be helpful.
This is no longer a problem. We now check that it is a JSEventListener before use.