Summary:
If a sprite object has multiple instances, and you first select it from the Object Bar, then click in the Animator tab, the IDE will crash. Sprites with only one instance will not produce this crash.
How to recreate:
Run the attached multiinstanceanimatorbug.cap and follow the instructions.
Note that this crash occurs when you click anywhere in the upper section of the Animator tab, or on one of the frames in the lower section.
Multi-instance animator bug example
LOL, I just "rediscovered" this bug, and came to the tracker to post it... only to realize that not only has it already been reported, it was in fact reported by me.
Completely forgot I even posted this thing.
Anyway, it's still happening in 0.99.42 but you probably already knew that :P