filesystems don't properly dismount

[Velcro Leaf]

Somewhere between 9.0-RELEASE and 9.1-RELEASE, something changed that 
makes it so filesystems on two of my servers with similar hardware don't cleanly shut down during soft reboots.

I only saw a couple 
examples of successful rebooting on 9.0 while transitioning from an 
earlier version to 9.1, but filesystems consistently complain during 
boot-up that they were not dismounted properly during every reboot in 
9.1.

Based on the release notes, it seems like it might have 
something to do with the new style of NFS.  Is the old style still 
latent in 9.1?  For example, can you recompile the kernel with different
 options to make the old style of NFS the default?  Am I barking up the 
wrong tree?  Any suggestions?

These are on mirrored RAID drives. 
 If you need other hardware details, please explain specifically how to 
collect the information.  I'm no hardware expert.  Thanks!