Can't umount a formerly mounted drive

I have two drives in a x86-64 machine.  Drive ada2 has current on it, and
drive ada1 has 9-stable on it.  At some point, while running current, I
mounted the /home partition from stable to copy some files and re-ipled
the system into stable.  every thing worked properly.  Some time later I
ipled current again.  I then noticed that the stable /home was mounted
on /mnt.  I tried to umount it but the operation failed as /dev/ada1p7
was not considered mounted.  Yet with out mounting I could access all
the files on stable's /home, I could create and delete files.  

The current system was cvsup'ed on Wednesday this week, while the stable
system was cvsup'ed last Sunday.  Neither system has exhibited any
hiccups.  Can somebody explain what has happened her on the current
system and how it should be corrected?
-- 
Best regards,
Derek Tattersall
dlt_at_mebtel.net		dlt666_at_yahoo.com		 dtatters_at_gmail.com