This is a problem which I bet running Disk First Aid won't help (but run it anyway, just in case). Just recently I was getting the strangest error when I tried to rebuild the desktop: when I clicked OK, it just went into the finder. The menubar was mixed up, and applications wouldn't launch right. Finally, I ran Norton Disk Doctor, which said my system file (8.51) had a damaged resource fork. So I reinstalled the system (from the 8.5 CD), rebuilt the desktop, and things worked fine. So anyway, I'd say to run some kind of disk repair application and see what's going on. Also, system 8.5 runs Disk First Aid automatically after a hard restart or improper shutdown. If you have that option turned off, it might be a good idea to turn it back on.
Patrick