That's what you get when you try to shoehorn the win32 API into X11... Since this is used in proprietary applications, you often won't know that they are using this toolkit until you hit some problems... You can tell that they are using a win32 API on X11 because you can find these weirdly named libraries:
The fix is simple once you know where to look, you need to set these 3 environment variables:
MWNOCAPTURE=true, see X hangs while debugging the application
MWNO_RIT=true, see X Server hang issues and MWNO_RIT
MWWM=allwmALLWM mode in MainWin: some of our customers feel that this windows look-and-feel is incongrous on a UNIX desktop.., In the ALLWM mode, MainWin? lets the window manager reparent, decorate, and handle user interactions rather than doing it through the MainWin? library.
You can also find this gem: So, the obvious question is, why don't we fix all this so that the ALLWM mode works flawless? Well, we tried it and we couldnt come up with a solution which works with all the window managers on different platforms.
r8432 adds these environment variables to the default config. (can be backported safely)
Note: we may still need to improve grabs (#139), but that is no excuse for an application to completely lockup the X11 server!
Backport in r8447. Closing.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/785