copying date to floppy

Long shot but....
Windows doesn't write info directly when you say to, most of the time it is cached (held in memory in case there is more to add). When you tried to copy your data it is remotely possible that windows figured it had better hurry up and finsih the first job and wrote the info from the first job to your floppy. Other person probably walked away with floppy with an empty data file!!!

Haven't seen this sort of thing since the days of 3.11 and win95.

regards
rick

Replace the FD.

Vaguely remember something like this from years ago. The problem was some sort of virus. What it was doing was the infected machine was copying the FAT table from the floppy, and then replacing subsequent disks's FAT tables with that.
If it's the same problem we had, then you'll find all the floppies you've put into that machine are unusable, as it's not really copying any data, just the "file list".
I think we got around this by just virus checking the machine (and destroy all the floppies you've used in it).
Good luck.