Created attachment 103690 [details]
Screenshot demonstrating the issue

When compositing is disabled, I can sometimes see a black square in the top-left corner.  I believe this is related to xembed-sni-proxy because clicking the black square behaves like clicking on one of the tray icons that are managed by xembed-sni-proxy -- both for left-click and right-click.  The square is not visible when compositing is enabled, but e.g. going to full-screen in mpv disabled compositing and then I have this square on top of the video.  Furthermore, *clicking* the area covered by the invisible square still behaves the same when compositing is enabled (naturally, as compositing does not affect input handling).

This is not 100% reproducible, I just restarted the application tied to the square (Gajim) and the square did not come back.

I will attach a screenshot demonstrating the issue.