The following bug has been logged on the website:
Bug reference: 9895
Logged by: Niels Kristian
Email address: nk(dot)schjoedt(at)gmail(dot)com
PostgreSQL version: 9.3.4
Operating system: Ubuntu
Description:
Hi I just realized that my data contains a few duplicate primary keys! There
has ALWAYS been a PRIMARY KEY constraint on those ID's. The affected records
might have been created while running a previous version of postgresql.