Hey Mike, thanks for the quick response.
Incredibly, from the moment I turned on Fraps the problem ceased to happen and I haven't been able to replicate it since.
I'll send you the video and the project as soon as the problem happens again, but in the meanwhile, do you have a theoretical idea why this would happen?
Keyframes were created automatically every time this happened, so it's not a keyframe issue. Could it be the bones not connected to the sprites properly?
Thanks,
Vukasin