The unix "du" command is lying to me on Sunos5 machines...
This is Sun bug 1234858; we were the first ones to discover it (I think my name appears in the Sun bug report...).
The Solaris 2.5 NFS V3 client and server both incorrectly handle the "disk space a file requires" information, in ways that cause the 2.5 client and server to work OK together, but cause the 2.5 client to work incorrectly with other V3 servers (including both ours and Digital UNIX 3.2C's, and probably most others) and cause the 2.5 server to work incorrectly with other V3 clients.
A customer who saw this reports that the Sun patch is 103477-06.
It also appears to be fixed in Solaris 2.5.1.
Any known work-arounds?
Use NFS V2 instead.
I checked NETAPPs' FAQ and didn't see anything.
Having answered this question several times, I asked people here to broadcast the answer more broadly; hopefully, it'll show up in our on-line FAQ.