Crashing under NFS load

I have one box running CURRENT from Feb 29.  It is a headless box, and 
acts as an NFS server sreving up /usr/src and /usr/obj for my laptop. 
Three times now, I have been doing something on the laptop (buildworld, 
most recently I just did an "installkernel") and the headless NFS server 
  stops working, and resets--it comes back up fine, and the nfs client 
resumes normally.

I've found nothing in any /var/log files that sheds a clue.

Is there anything I can do to identify the problem?  I'm in the process 
of updating to the latest current to see if that fixes it.

Scott