umount: it seems [device] is mounted multiple times

i was finishing up a job with a compact flash when, trying to unmount it:

#> umount /dev/sda2 
umount: it seems /dev/sda2 is mounted multiple times

Looking at what mount says:

#> mount | column -t | grep sda2
/dev/sda2  on  /mnt/flashrw  type  ext3      (rw,nosuid,nodev)
/dev/sda2  on  /mnt/flashrw  type  ext3      (rw,nosuid,nodev,user=myuser)

it seems that I accidentally mounted the same device on the same location (though in two different ways).

I tried to unmount it many times also with:

#> umount /mnt/flashrw 
umount: it seems /mnt/flashrw is mounted multiple times

with no luck. Finally, I tried:

#> sudo umount -f /dev/sda2

but umount locked completely.

So the question is: and now?

Try running this command:

sudo umount /mnt/flashrw