That's another issue; it's clearly a bug for the filesystem type to
override the ability of the system to try* to mount a device.  Unix has
historically given one rope enough to hang oneself with; I personally
mind not being able to just say "look, I know it doesn't *say* it's a
ufs filesystem, but believe you me, it is."  Not that I'm coexisting with
SVR4 right now, but I did for quite a while.

-s