Hi again, I can pinpoint now my problem to a tandem of xserver-xorg-video-nouveau (either in current stable and testing/unstable) and xfwm4 in version 4.12.
More specifically XFWM in recent version (4.12): 1. triggers problem when used with nouveau 1.0.11 [b1] and G92. 2. works OK with nouveau 1.0.11 and G86 3. works OK with Intel graphics. There are several points in XFWM changelog that looks suspicious (like https://bugzilla.xfce.org/show_bug.cgi?id=8898 applied in 4.12), but no clue what to investigate further. Best regards -- Jacek Kawa
