fungus:
The only thing I can think of is a batch of chips got sent out with incorrect fuse settings. The setting allowed people to overwrite their bootloaders. Rewriting the bootloader would set the fuses correctly, preventing them from being able to reproduce the problem.
But like I said earlier with the older bootloader,
it was possible to enable WDT and create a situation where it was not possible
to upload a new sketch using "normal" means.
When the bootloader was re-written it also removed the sketch and things worked as "normal" again.
-- bill