Mounting DOS discettes in FC4

[Uno Engborg]

Hi!

I have problem mounting MS-DOS discettes from Gnome. The discettes are 
handled by an USB discette unit from Acer.
The unit seams to be recognized when connected, as the drive makes some 
sounds indicating that it is trying to read the discette, and the Gnome 
icon in the Computer folder changes to a disk with an USB stick.

However, when I double click the disk it refuses to mount. The error 
dialog tells me that it need to know the file system type.

The same thing happens from the command line if I do

mount /dev/sda /mnt

but if  I do
mount -t vfat /dev/sda /mount
everything works fine.

I do have vfat listed in  /etc/filesystems, so why do I need to specify 
the filesystem  type?

Any suggestions on what I'm  doing wrong, or is this a bug?

Regards
Uno Engborg