I use a file as a filesystem volume using the loop device,
the fstab entry looks like this:
	<myfile> <mountpoint> ext2 loop,user,noauto 0 0

I mount/umount this volume frequently as an ordinary user.
I noticed that after umount, the corresponding device /dev/loop0,
loop1, loop2, etc. gets not freed; after several umounts no loop
devices are left available and mount command fails. To correct it
I had to run losetup -d.

When root umounts the volume, everything looks fine.
The kernel is ver 2.2.11.