Bug#298595: it's a BIOS problem
> Does this mean that, being indeed a BIOS problem, this bug report can
> be closed...or not immediately?
It didn't quite get to the debian installer proper, so it is
unclear what can be done from within the boot image. (I reckon that a
general purpose USB storage driver set is a bit too much to cram into 512B
of the MBR :) ). Therefore, it seems that it's OK to close the bug. It's
there mostly for archival purposes, as with other installation reports, so
that anybody else with similar symptoms knows what to do.
I'll now go and fetch the motherboard/BIOS version specs.