You may want to have a look at
http://www.NetBSD.org/cgi-bin/query-pr-single.pl?number=4723

The patch in that PR didn't help me, but I didn't have the opportunity
to investigate further.  I no longer have the configuration described
in the PR, so I can't do any further testing.  But maybe it will give
you some ideas about the cause of the problem.

--
entropy -- it's not just a good idea, it's the second law.