After upgrading my system to 5.2, the following command
failes:

mformat a:

with the message:

[root@loki mtools-3.9.1]# mformat a:
mformat: Non-removable media is not supported (You must tell
the complete geometry of the disk, either in /etc/mtools or
on the command line)

This used to work, of course.  In fact, it works on a 5.0
system with the same floppy.