I've had this happen several times during my current project. The animation frames lose their picture and image points are gone too (I think). I only find out when I play the game and see a big error message out of nowhere. I think mine happened for the same reason as yours.
I tried to reproduce this with a new project, and it did as he said.
I also noticed that if you do NOT save right after renaming, that it does not create this error. If I preview it without saving, it usually works. So renaming the animation, then saving seems to be the issue. Of course, I don't know if saving later will have any effect, so I don't want say for sure.
Also, it does not seem consistent, but I was able to get the error to pop up multiple times while trying.