Error unmounting the floppy - "/usr/bin/pumount" (Permission denied)

[agenteo]

Hi,
I've mounted the floppy from Computer -> Disks double clock on the 
Floppy icon. I've got an error while unmounting the floppy from the 
GNOME desktop.
In english it's something like:
Error while unmounting
Command failure
Impossible to execute the child process "/usr/bin/pumount" (Permission 
denied)
I really don't know what could it be. If I try a sudo umount 
/media/floppy0 everthing is fine... but I can't do this all the times.
This are the groups where the user is:
agenteo adm dialout cdrom floppy audio video plugdev lpadmin scanner
I didn't
this is the /etc/fstab floppy's line:
/dev/fd0        /media/floppy0  vfat    rw,user,noauto          0       0

Thanks in advance,
Enrico