This happened to me with a 1.0_BETA ~20. Aug.: I was copying some large 
(X screen dump) files from the BSD partition to the DOS partition, which is
mounted az an MSDOSFS filesystem, when I filled the disk (the DOS part of
course). Cp came up with a strange error message (E2BIG, and not ENOSPC
for the files it wasn't able to copy and ls gave just garbage as the MSDOS
root dir.

Switching back to dos revealed that the boot record, the root dir and part of
the fat has been overwritten. I suspect that the data on them 
was from the files being cp'd, but I'm not sure.

Has anyone seen anything like this?

Fortunately Norton Disk Doctor did a pretty good job in reconstructing.

I'm sorry that I'm not giving more detail, but there are some valuables even on 
the DOS side, so can't affort experimenting with it, thus I didn't try
to reproduce the error.

The machine is a 486DX2/66 8M RAM, 420 M IDE wd caviar. The DOS partition is 
a MS-DOS5.0. I know that the man for msdosfs says that 5.0 hasn't been tested,
but I don't this this is the cause. 

- szabolcs