I just tried xemacs 21.4.3 version with gtk and mule
enabled.
 In previous version - 21.1.14 + athena there was possibility to copy
 and paste under X Window using mouse (left to copy; middle to
 paste). In 21.4.3 + gtk this doesn't work while info page (Using X
 Selections) still says that's possible.
         I don't know if this is generic problem with all gtk versions,
 with all 21.4.x beta series or just my local emacs problem.
 Any suggestions/patches how to enable/fix such copying in X Window? 
Known bug - we should probably document it in etc/PROBLEMS.  It happens in
the 21.5 series as well - I just haven't been able to track it down.  I
imagine it is something stupid on my part when I did the 21.4 GTK merge.
The mouse and selection handling changed drastically from 21.2, and I
probably just missed something.
I will try to take a look at this tonight - the wife is going out, and liam
is getting ready for bed.
-bp