I said:
> I think the guilty party is the pfree() in dist_pb.
Indeed, removing the pfree call at line 2254 (in 7.2 sources) of
src/backend/utils/adt/geo_ops.c makes the problem go away.
I am working on a more extensive patch in hopes of fixing possible
similar errors elsewhere in this file, but that should get you going.
regards, tom lane