umount: not coherent with fstab

[Luca Ferrari]

On Tuesday 22 May 2007 Mitch Contla's cat, walking on the keyboard, wrote:
> Why dont you type 'mount' and see how the os thinks the file systems are
> mounted. Maybe this will give you a clue as to why your umount is not
> working. Are you using umount as root?

The mount command reports me the filesystem is ok with fstab. If I umount as 
root it works, then I can re-mount as normal user, but cannot umount as 
normal user. But the mount point belongs to the user and my fstab contains 
the users option:

# /dev/sda12
UUID=E63F-7400  /mnt/disco2     vfat    
defaults,utf8,umask=000,users,exec,suid 0       1


[luca at fluca:~]$ mount | grep disco1
/dev/sda11 on /mnt/disco1 type vfat (rw,nodev,utf8,umask=000)


What am I missing?

Thanks,
Luca