umount problems with multiple mounts

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

hey,

yes, my fault, but:

%mount 
/dev/ad6s1a on / (ufs, local, soft-updates)
/dev/ad6s1b on /pbulk (ufs, local, soft-updates)
/ on /pbulk/clients/labospc67_1/root (null, local, read-only)
/pbulk/clients/labospc67_1/var on /pbulk/clients/labospc67_1/root/var (null, local)
/pbulk/clients/labospc67_1/tmp on /pbulk/clients/labospc67_1/root/tmp (null, local)
/pbulk/clients/labospc67_1/dev on /pbulk/clients/labospc67_1/root/dev (null, local)
/ on /pbulk/clients/labospc67_1/root (null, local, read-only)

%umount labospc67_1/root
umount: unmount of /pbulk/clients/labospc67_1/root failed: Device busy

%umount /pbulk/clients/labospc67_1/root/var
umount: unmount of /pbulk/clients/labospc67_1/root/var failed: Invalid argument

something is wrong here.  i guess I can't umount the "upper" root mount, because it takes the "lower" root mount first.  dito for the subdirs.

cheers
 simon