Some further information on this bug. It turns out that it does not only appear during video playback, but also happens for windows that are animating, or moving large amounts of graphics data in other ways.
For example, the "coverflow" area of a Calibre window can demonstrate the behaviour, as can a browser window which is rapidly moving (i.e. Google Street View, when moving around).
Currently installed versions of X packages are:- ii x11-xserver-utils 7.7~3 amd64 ii xserver-common 2:1.12.4-5 all ii xserver-xephyr 2:1.12.4-5 amd64 ii xserver-xorg 1:7.7+2 amd64 ii xserver-xorg-core 2:1.12.4-5 amd64 ii xserver-xorg-input-all 1:7.7+2 amd64 ii xserver-xorg-input-evdev 1:2.7.0-1+b1 amd64 ii xserver-xorg-input-synaptics 1.6.2-2 amd64 ii xserver-xorg-input-wacom 0.15.0+20120515-2 amd64 ii xserver-xorg-video-intel 2:2.20.14-1 amd64 Mike -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org