This is a replication of a bug at launchpad, which currently affects 20 users[1].

I am opening here in hope for possible feedback from devs. Please note that the bug potentially was fixed in the development versions (see below).

Short summary:
In inkscape, simply clicking on the workspace will crash Xorg, and throw the user back to login screen. For a detailed error message, please refer to the launchpad bug.
This bug seems to be related to disabled touchpads - all affected users used laptops. Enabling the previously disabled touchpad will prevent the crash. For some users, disabling the touchpad via software would not cause the crash, while for others there was no difference. Due to this correlation with input hardware, a bug in inkscape itself seems unlikely.

The bug disappeared with switching to the xorg-edgers ppa in Ubuntu, but it is unclear exactly why. 
The bug was still present in the following xorg-edgers package og xserver-xorg-core:
2:1.13.0+git20120920.70e57668-0ubuntu0ricotz
and disappeared in 
2:1.13.0.901+git20121123+server-1.13-branch.c0e68f8e-0ubuntu0ricotz~quantal


As very similar issues were reported before in launchpad[2] and declared fixed, there might be an underlying root cause which is still open.


Links:
[1]: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1081108 
[2]: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1023004