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(at)endpoint(dot)com
End Point Corporation
PGP Key: 0x14964AC8