One of my colleagues from the Windows 95 project reminded me of a problem that I was called to debug. If the floppy drive was in use, the display driver was more likely to crash.
It wound up being a race condition between the floppy driver and the display driver. This is a race the display driver wouldn't normally expect to lose.
The problem occurred on machines running the kernel debugger. When the kernel debugger was connected, the display driver printed diagnostic information, which was sent over the serial port, which slowed down the display driver and made it more likely that the floppy drive would interrupt it at a bad time.