The screen flickers and then shows what seems to be old screen contents (most of the time it's the lock screen, but other times it's other things) on the background and the various elements of focused window are painted on top of that. See a video of the bug here: http://www.youtube.com/watch?v=2XymS3P29D0 Sometimes mouse movements trigger it, but other times it happens without keyboard or mouse input. Switching to a different virtual desktop solves the issue, but it often happens again when I switch back.
Which version of xfwm4 (xfwm4 --version)? Does the same occurs without the compositor enabled?
(In reply to Olivier Fourdan from comment #1) > Which version of xfwm4 (xfwm4 --version)? Does the same occurs without the > compositor enabled? Version 4.12.4 (revision 7844952). This has been occurring for a long time though, at the very least 1 year, maybe 2. When the compositor is disabled it doesn't occur. Also certain things prevent it from happening. For instance, when I tried to record the bug with the vokoscreen screen recorder it wouldn't occur, whereas when I used byzanz (another screen recorder) it did. Tried several times with each to be sure, every time I was recording with vokoscreen it wouldn't happen, every time I was recording with byzanz or not recording it did happen.
I doubt this a bug in xfwm4 though, which Xorg version/driver/hardware do you use? Can you try with the modesetting driver and see if this happens ?
(In reply to Olivier Fourdan from comment #3) > I doubt this a bug in xfwm4 though, which Xorg version/driver/hardware do > you use? > > Can you try with the modesetting driver and see if this happens ? X.Org X Server 1.19.2 with the radeon driver. On the xfce mailing list other users have reported the same problem with nvidia hardware (see "screen not repainting" thread), so it probably isn't a driver/hardware-specific issue. I will try the modesetting driver and report back.
(In reply to Olivier Fourdan from comment #3) > I doubt this a bug in xfwm4 though, which Xorg version/driver/hardware do > you use? > > Can you try with the modesetting driver and see if this happens ? After using the modesetting driver for 3 weeks, haven't seen the bug again. This strongly suggests you were right, it's a bug in the radeon X driver, unrelated to xfwm.