Comment 4 for bug 201535

Thanks for reporting this bug, but unfortunately the backtrace generated did not have the information necessary for troubleshooting it. Please install the debug packages for the xserver and try reproducing the crash. More information on gathering complete backtraces is available at https://wiki.ubuntu.com/DebuggingXorg as well.

Offhand, my assumption is that this is a dupe of either bug 194249 or bug 193559, however lacking a better backtrace it's impossible to say for certain.