Comment 48 for bug 555408

Now this is where it gets odd. Yes, my user is in the virtualbox group, as I am a vbox user. But.... I don't have this issue with Rhythmbox.

Starting a guest session and then starting shotwell confirms your assumption. Mouse works flawlessly as a guest user. On the other hand, just unloading the vbox-modules didn't help (using rmmod).

I'd say, pretty good guess! Confirmation hereby given.