It was not as catastrophic as the Apple 13 to
16-sector conversion,
but for a brief time, there was some media chaos in the PET world.
The worst problem with the CBM PET drives IMHO was that the 8050 could
not read (or write) the disks from the older drives (like the 4040), and
that there was no easy way to copy certain types of files (I think one of
the random access data file types) between drives in different units.
Which meant there was no way to copy such a file from a 4040 disk to an
8050 disk. And which, in turn, meant you really needed both types of
drive unit conencted to a PET.
At least the Apple ][ 16 sector controller could read 13 sector disks
with special software.
-tony