Has anyone else used the union mount filing system?

I have stopped using it now. I am not certain that it was resonsible, but
strange things started happening after I had put a union mount entry into
/etc/fstabs to mount /usr/tmp over /tmp (so that gcc would have enough
space).

On two occasions a directory on the /usr partition had its inode info
messed up, so that it appeared to be a Block device with huge major and
minor device numbers. The first time it happened it was back to normal
when I rebooted, the second time, it didn't go away, and fsck spent ages
finding disconnected files that used to be beneath the affected directory.

	Andrew