"could not reattach to shared memory" captured in buildfarm

vaquita has an interesting report today:
http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=vaquita&dt=2009-05-01%2020:00:06

Partway through the contrib tests, for absolutely no visible reason
whatsoever, connections start to fail with
FATAL:  could not reattach to shared memory (key=364, addr=02920000): 487

We've certainly heard more than a couple of field reports of this from
Windows users, but I don't think we've ever seen it in the buildfarm
before.  (I don't see any similar instances in vaquita's history, anyway.)

I assume vaquita's configuration hasn't changed recently (Dave?)
so this seems to put the lie to the theory we've taken refuge in
that it's caused by bad antivirus software.  I don't see that it
gets us any closer to a solution though.
        regards, tom lane