grub copying screen to printer?

[Tom Horsley]

Twice now, I have had one of my boot partitions corrupted in this strange
fashion:

The word GRUB appears on the screen, then the system proceeds to copy
the contents of the screen to the printer port over and over.

Re-installing grub from rescue disk fixes the problem and all seems
to be well otherwise.

Copying the screen to the printer seems like awfully complex activity
for any kind of random corruption to achieve. Anyone have any notion
what the heck is going on here?