Btree or not btree? That is the question

We have a 8.3.18 system (yes, the same one from the previous 
thread, finally upgraded!) that gave us this error yesterday:

ERROR:  index "pg_class_oid_index" is not a btree

It seems like this happened from just a normal SELECT query, and did 
not occur again (and this is a very busy system) The pg_class table 
does gets vacuumed and reindexed often. All appeared fine when I 
did some manual investigation.

Since this only happened this one time, can I chalk it up to 
some random rare race condition having to do with a reindex? 
Or is there anything else I should be looking for or can 
proactively do? No other system catalog problems have been seen 
before it or since.

-- 
Greg Sabino Mullane greg@endpoint.com
End Point Corporation
PGP Key: 0x14964AC8