There are many bug reports about this problem:

A Debian bug report filed against xserver-xorg-video-qxl package also mentions a thread on our forum.[1] The problem is acknowledged and fixed upstream because it was also experienced in fedora.[2] The changelog for the Ubuntu release lists a fix for disabling surfaces included in (Debian) 0.1.4.[3]

• Resync on Debian, grabbing new upstream release 0.1.4 (LP: #1474154).
• Take some patches from Fedora. + debian/patches/qxl-kms-disable-composite.patch: Fix graphical glitches by disabling COMPOSITE extension. (LP: #1261916) + debian/patches/no-surfaces-kms.patch: Should fix crashes.

The current stable version is 0.1.1. Debian Testing has 0.1.4 that includes the fix.[4]

[1] https://bugs.debian.org/801081

[2] http://spice-space.org/page/XorgQXL

[3] https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-qxl/+bug/1474154

[4] https://packages.debian.org/search?keywords=xserver-xorg-video-qxl&searchon=names&suite=all&section=all

Yet another example of why Stable is a PITA. Non security bugs can afflict users for years at a time because package versions are ossified. Yay Stable! :P

Awesome write-up. Can you please reference this ticket from the relevant places (package description, documentation, forum, w/e) so no one will again wonder (and create a ticket :)? Then this can be considered very much done.

Linked relevant topics. Feel free to close this ticket unless there is something else.