I can't shed any more light on your predicament, but I can confirm
that I've experienced something almost exactly like what you
describe on an x86 (specifically, 200MHz PPro) running 2.1.65 (with
Rik van Riel's now deprecated vhand patch). Curiously, I didn't
get it on every boot attempt - I only saw it three times, but two of
those were on first boots of freshly built kernels. The third may have
been, but I cannot remember precisely.
I've yet to see this on 2.1.72 (but I'm judging from an inadequate sample
of 1 boot).
Keep well,
Stephen Thomas