Everyone and his dog seem to call libxml2's xmlCleanupParser() at inappropriate places. For example Empathy does it, and Abiword does it too. Google Code Search seems to reveal at least Inkscape and Dia do it as well.
So, please, if your project links against libxml2 verify that it calls xmlCleanupParser() only once, and right before exiting! And if it calls it more often or somewhere else, then please fix that!
For more information see my post on fedora-devel.
Thanks for your time.