Testing with a 0.15.0 r8892 windows client against a 0.15.0 r8872 fedora 20 server... I think I finally found the repro for this elusive bug (which does not manifest with the 0.14.x branch).
The top level-focus issue only shows itself after clicking a "restore session" button on firefox (which shows when you restart the browser after having closed it in an improper fashion, either by just using a command/control-C from a launching xterm, or just by terminating a session server side with a control-C... or whatever).
To reproduce:
The initial window will close, and a new window will be opened in the saved location of the previous session window(s)... and this/these will not relinquish top-level focus (unless you use the "raise windows" option from the tray, which sometimes fixes for one "toggling", and sometimes fixes apparently indefinitely).
I'll attach an xpra info from before and after as well.
xpra info before restoring firefox (expected focus behavior still)
xpra info after firefox session restore (misbehaving focus)
I'm pretty sure that's the same bug as #713. (and I had tried to reproduce it - unsuccessfully)
Can you provide the -d metadata,window of just when this happens on the client side?
D'oh ... I believe you're right, this is the bug in #713 (I thought the ticket I'd tested this on was closed already).
I will close this and provide a log in #713 with -d metadata,window in the general vicinity of when this happens client side.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/829