Thanks for the reply.
I should have mentioned that I wasn't using Unity on that installation; my employer's proprietary software is completely messed up under Unity, so I was using Gnome 2. I did, however, install Calibre from the Canonical repository. I will try both versions in both environments today.
Your statement about Qt causing X to crash under Unity is very enlightening. That might just explain every session crash I experienced on that machine. Perhaps it's not entirely our Linux development team's fault after all.