freebsd stable - May 2005 - "Giving up on 2 buffers" message when rebooting while ext2fs mounted

Hi all,

I've just installed my FreeBSD system and upgraded it to the lastest
-STABLE with buildworld .

I have an EXT3 partition on my second harddrive that I mount read-only
with the command :

mount -o ro -t ext2fs /dev/ad1s1 /mount_point

The problem is that if I reboot without umounting that filesystem I
get this message on reboot :

syncing disks, buffers remaining... 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
giving up on 2 buffers

After the reboot the file systems are considered "unclean" and checked
with fsck.

If I umount the ext3 filesystem before rebooting I get the "No busy
buffers" message and all is fine .

What is causing this?

Thanks

Marcello