Upon upgrading to mesa 8.0, kwin_gles is not able anymore to perform blur effect. Cf. kde bug 294468 https://bugs.kde.org/show_bug.cgi?id=294468
Can you bisect?
I dont know, I am no expert :(. But I can try : what do you need me to do?
Problem has disappeared on a fresh install... I guess there was an update issue with some files from mesa 8.0
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