bug#18722: Correction

[martin rudalics]

>> I see something similar when I minimize the maximized window of another
>> application and (presumably, implicitly) re-focus the Emacs window.  But
>> I have no good recipe to trigger it reliably.
>
> I think we are relying on X expose events in these cases.  Maybe this
> particular window manager doesn't send them?

The problem is fairly new.  I think I noticed it about a month ago.  And
I didn't change my window manager in the past year.  But I might have
changed some of its settings :-(

The behavior seems time related: The longer another application's window
covers that of Emacs, the higher is the probability that the Emacs frame
is not redrawn.  Clicking on a menu item, resizing the frame, or
switching do it via M-TAB gets it out of the situation.  Clicking with
the mouse into the frame doesn't.

martin