I was trying to backup some files onto the floppy before upgrading to NetBSD1.0 
   Release, and may have found a bug.  While copying a file to my 1.44M floppy, I 
   mounted CD to look at some Photo CD files that I just purchased.  I got an error
   message(I should have made copy sorry, but this can easily be reproduced) saying
   that it could not write to a sector.

If you got a message from the kernel, you should *ALWAYS* include it
in your `bug' report.

Anyway, I suspect it was a `soft error' message, which is non-fatal.
The floppy controller is `designed' such that you are almost
guaranteed to get DMA {over,under}runs occasionally if another device
is doing DMA at the same time.