I've just noticed that when I enter a wrong password with "mount -o loop,encryption=AES128", mount exits with an error being unable to recognize a filesystem and leaves an active loop device behind. So that after repeating the mount with a correct password, "losetup -a" reports two active loop devices for the partition (only one mounted, of course). When mount fails, it should also delete the loop device that was created by the "loop" mount option.
While this is primarily a problem of util-linux 2.19 mount, it does not seem to happen with
non-encrypted failed "mount -o loop".
I'm using loop-aes-3.6c and util-linux 2.19
(OpenSUSE 11.4 with 2.6.37 kernel)