Yesterday I was about to suggest that the 300Kbps/300rpm mixup might be
the problem, but I figured that it would surface eventually.
IMD does have an RPM-checking routine--I use it frequently when
modifying 2.0MB 3.5" drives to masquerade as 1.6MB ones. It ensures me
that the result will behave as intended.
The difference between 300 and 360 RPM is on the hairy edge of the
capture range of most data separators, so simply reading a floppy is no
guarantee of success when writing one that's been formatted at the
incorrect bit clock/rpm rate.
But I'm certain that you've been adequately instructed by experience and
will sin no more... :)
All the best,
Chuck