8940 doesn't understand the tag namespace after some times of using

I'm using 8940 on Windows XP Pro SP2. I'm using RichFaces 3.2.2.GA which has tld files for the a4j and rich tags.

After using 8940 for a while, 8940 doesn't understand the rich tag (although it understood it before). If I close Idea and run it again, everything is fine. I even cleared the cache (delete everything in .IntelliJIdea8.0/systems) but that didn't help.

Does anybody know the reason?