NFS, got bad cookie, and Bonnie++

When using FreeBSD as a client, bonnie++ over NFS fails.
Server software does not appear to matter. Bonnie dies if the server is
another FreeBSD machine, localhost, or a Linux-based SNAP appliance.

Note that bonnie++ with Linux as a client does *not* fail.

backup# bonnie++ -u 0 -s 2 -r 1
Using uid:0, gid:0.
Writing a byte at a time...done
Writing intelligently...done
Rewriting...done
Reading a byte at a time...done
Reading intelligently...done
start 'em...done...done...done...done...done...
Create files in sequential order...done.
Stat files in sequential order...done.
Delete files in sequential order...Bonnie: drastic I/O error (rmdir): Directory not empty
Cleaning up test directory after error.

And the Bonnie.pid directory is left behind with 8000+ empty files in it.

These (and many more) are logged on the client the moment "Delete files
in sequential order" is printed by Bonnie:
Dec 16 09:34:43 backup kernel: got bad cookie vp 0xc298d920 bp 0xc7723c78
Dec 16 09:34:44 backup kernel: got bad cookie vp 0xc298d920 bp 0xc76964e0

There is a PR that discusses this "got bad cookie" issue:
http://www.freebsd.org/cgi/query-pr.cgi?pr=33203

Matt Dillon suggests that the "got bad cookie" messages are informational.
Nonetheless, Bonnie++ dies with FreeBSD as a client but not (at least)
Linux.

Is this a Bonnie++ anomoly? It is hurting our confidence in FreeBSD NFS in
a big way.

Any insight would be greatly appreciated.

-- 
Charlie Watts
cewatts_at_frontier.net