TRAP: FailedAssertion("!((itemid)->lp_flags & 0x01)", File: "nbtsearch.c", Line: 89)

I've got a customer who was having a problem with a backend running away
with memory. It would hit 46G before finally being running the box
completely out of memory. It didn't appear to be related to hashjoin/agg
or pending triggers, so I had them recompile with debug and assert
turned on. A bit after restarting we get:

TRAP: FailedAssertion("!((itemid)->lp_flags & 0x01)", File: "nbtsearch.c", Line: 89)

Looking through the code I see that's something to do with indexes, but
I'm not sure what. Is this likely a corrupted index? If so, is there
some way I could identify which index?
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461