a df option question

I have a couple of students using Mandrake on laptops
who reported to me that df -B MB is a valid option for
df on their system. They even supply output showing
what it does.

I've never heard of such an option in any version of
Unix I've ever used. Mandrake is based on Red Hat,
which uses the GNU tools for all the most standard
utilities, right?

Does anyone know anything about this? I'd love to see a
df(1) man page off a Mandrake system.

--
Lynn David Newton
Phoenix, AZ