Comment 6 for bug 232476

The locking assertion failure sounds like bug 185311.

Since we're seeing a few issues with traces involving libxcb, I've prepared a non-xcb-enabled libx11 here: http://people.ubuntu.com/~bryce/Testing/libx11/ . (I'm not certain I reverted all the deps correctly, so let me know if there are dependency-related issues with this. You probably should save your old libx11 debs in case the lack of xcb causes problems in other apps.)