Comment 9 for bug 529502

i have this issue too on lucid with cryptsetup 2:1.1.0~rc2-1ubuntu13 although the suggested work-around does not work for me. i've plugged in an external disk taken out of another ubuntu installation:

$ sudo cryptsetup luksOpen /dev/sde5 sde5_crypt
(this makes available the -root and -swap partitions in /dev/mapper)

$ sudo mount /dev/mapper/laptop-root /mnt/laptop-root
(now i have just moved some files from the partition and am ready to unmount)

$ sudo umount /mnt/laptop-root/
$ sudo cryptsetup luksClose sde5_crypt
Device sde5_crypt is busy.
$

is there any way to cleanly remove the drive without shutting down the whole system??