8.0 -> 8.1 dump duplicate key problem?

I have an interesting situation...am staging a mock upgrade from 8.0 to
8.1 on a bzip compressed backup image from one of our production
servers. The dump image is big (270 mb compressed) and so is the file
in question ~ 440k rows.

Am piping the backup image to the server via
psql -cd backup.bz2 | psql zyx

When the dump gets to the point where the indexes/keys are built, the
primary key fails to build due to duplicate key constraint failure.
However, after dump is complete, I can create the p-key without any
modification to the table and everything is fine.

The error is reproducible...I have confirmed in two separate runs. The
source 8.0 database is still up and does not report any dups in the
p-key fields, which of course it shouldn't.

Merlin