When you've finished renaming it, what do you do? I seem to recall that if you just click outside of the textbox, it will revert to the previous name, but if you actually hit Enter, it will save the new name. It's been a while since I've tried this though,
and I'm only responding from my phone at the moment, so I can't check, but I'm pretty sure that I've run into something like this before.
If you've tried hitting Enter and still had it not save the new name, check the server logs to see if it encountered any permissions error or any other exception at the time.