Comment 12 for bug 594144

from the release notes of Snapshot 1.9.12 (2010-07-12):
<quote>
Bugs fixes
----------

  https://bugs.launchpad.net/ubuntu/+source/cairo/+bug/600622

    Inkscape was caught in the act of attempting to modify a finished surface.
    Unfortunately, we had the ordering of our guards and assertions wrong and
    so an ordinary application error was triggering an assert in Cairo. This
    lead Benjamin to add a test case to ensure that the entire public API
    could handle erroneous input and then proceeded to fix a whole slew of
    uncovered bugs.
</quote>
<http://lists.cairographics.org/archives/cairo-announce/2010-July/000160.html>