when a transient window (ie: a pop-up/down menu) is shown in another window, we can move the parent window which leaves the transient window behind in the wrong place... We'll need to find the relationship between the windows and move them by the same amount, which is going to be hard.
fixed in r464
(we now also correctly set the window hints for transient windows)
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/58