Duplicate records leaking into unique indexed tables

Doug Mitchell (pgsql(at)dougmitchell(dot)com) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
Duplicate records leaking into unique indexed tables

Long Description

PostgreSQL 7.0.3 on RedHat 7.0

I have some fairly large (2-3 million rows) tables with a PRIMARY KEY that created a valid unique index. After a few days of high-concurrency updates, vacuum says the it "can not insert a duplicate record into tablename_pkey". I'm fairly sure that my application would crash if an INSERT failed due to key duplications, so I have to believe that this is internal to PG. Maybe the index is pointing to both the current and a previous version of the same tuple.
I didn't see this until I upgraded from 7.0 to 7.0.3, but I was not looking for it.

Thanks,
Doug

Sample Code

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