Discovered as part of #2167: injecting random errors into the paint code correctly logs the problem both client side and server side (now with the stacktrace), and the server is notified of the decoding error, yet thing aren't reset properly and eventually the server shows:
Warning: timeout on screen updates for window 1, already delayed for more than 15 seconds
patch to trigger errors
The fix is in r21806 - triggering this problem is actually almost impossible, so no big deal.
Related improvements in:
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2168