https://bugs.freedesktop.org/show_bug.cgi?id=92952
--- Comment #8 from EoD EoD@xmw.de --- Can't you disable the postprocessing AA when MSAA is enabled? Or at least give a huge warning/error message in such a case?
It took me a very long time to figure the problem out (neither an error, nor any other way of telling me the correlation) and I am pretty sure there are many more people out there encountering the bug.