ext2fs marked dirty when mounted read-only

[hardware at ee.ccny.cuny.edu]

Dear FreeBSD Filesystem List,

When I uncleanly unmount an ext2fs filesystem that is mounted read-only
it needs to be fsck'ed before the kernel will allow it to remounted.

kernel: 6.1-RC1 FreeBSD 6.1-RC1
disk: da0 at umass-sim0 bus 0 target 0 lun 0
      da0: <ST350084 1A 3.AA> Fixed Direct Access SCSI-0 device
      da0: 40.000MB/s transfers
      da0: 476940MB (976773168 512 byte sectors: 255H 63S/T 60801C)

When I try to mount the ext2fs filesystem in read-only mode, I get this:

      WARNING: R/W mount denied.  Filesystem is not clean - run fsck

This problem can be reproduced on my system by the following steps

	1) mount -t ext2fs -o ro /dev/da0 /mnt # da0 is external USB
	2) ls /mnt
	3) UNPLUG THE EXTERNAL USB DISK
	4) reboot
	5) mount -t ext2fs -o ro /dev/da0 /mnt

thanks, -kurt