vfs.usermount=1, bug?

Hi, 
using freebsd5.2-release 
I've set vfs.usermount=1 in sysctl.conf. 
Normal user get permission denied when trying to 
mount an ntfs permission (slice ars01), until root 
has mount and umount it at least once. 
See the following 
 
File permission on /dev/ar0s1 is 644 and owned by 
root:operator 
 
User ddais member of group dda, wheel & operator. 
 
A) Mounting as user dda: 
dda_at_work:~> mount_ntfs /dev/ar0s1 mnt/ntfs/ 
mount_ntfs: /dev/ar0s1: Operation not permitted 
 
Mounting was not permitted  
 
Changing to root: 
dda_at_work:~> su 
Password: 
ROOT_at_work:/home/dda# mount_ntfs /dev/ar0s1 
mnt/ntfs 
 
Slice was mounted without problem, let's umount 
it, and change back to user dda. 
ROOT_at_work:/home/dda# umount mnt/ntfs 
ROOT_at_work:/home/dda# exit 
exit 
 
B) TRY AGAIN NOW AS USER DDA 
dda_at_work:~> mount_ntfs /dev/ar0s1 mnt/ntfs/ 
 
NOw it works?! Hmm...!? 
 
Any suggestions?! 
Thx