JRex Dom Implementation: Node.setUserData

Hi,

i retrieve a loaded document from jrex via 
browser.getNavigator().getDocument() and now
i want to add user data to nodes with the following method of Node:
public Object setUserData(String key, Object data, UserDataHandler handler);
The problem is the call to setUserData never returns. I have looked into 
JRexNodeImpl.setUserData but this method calls a native method 
SetUserData, which i do not understand.

Did occure this problem to anyone else?
Or can someone guess where the problem might be?

Thanks in advance,
Jochen