Upgrade mount and umount to the 0.95(a) versions: the 0.12 version opens
/etc/mtab~ with O_CREAT | O_EXCL, but no O_WROLNY, so writing to the
file will fail (and mount doesn't check for it). The 0.12 kernel didn't
check for the open-mode when writing, so it worked for that, but 0.95a
does.
Linus