Automount + NFS: frequent hangs new in FreeBSD 6

[Geoffrey Mainland]

I'm running an NFS server (5.4) and a client (6) that uses amd to mount
the NFS shares from the server. I've been doing this for quite a while
without any problems (before upgrading the client to 6). However, after
the upgrade high file system load causes amd to hang often--I get a
"pid123 at blahblahblah not responding" message and amd is unresponsive for
a minute or two. Mounting the same NFS shares *without* amd works just
fine with the same usage pattern, so the problem appears to be with amd
itself and is specific to FreeBSD 6. The client is using the BSD
scheduler and has all debug.mpsafe* sysctls set to 1 (the problem still
occurs when these sysctls are set to 0).

Has anyone had similar problems?

Thanks,
Geoff