https://bugs.freedesktop.org/show_bug.cgi?id=93591
--- Comment #4 from EoD EoD@xmw.de --- (In reply to Nicolai Hähnle from comment #3)
Based on an analysis of the trace I've done some time ago this is a pixel discard problem, most likely the same as bug #93594.
*** This bug has been marked as a duplicate of bug 93594 ***
I am not surprised, thanks for looking into it :)