The following bug has been logged on the website:
Bug reference: 12432
Logged by: Brian Quirion
Email address: bquirion(at)gmail(dot)com
PostgreSQL version: Unsupported/Unknown
Operating system: Linux
Description:
foodb=> select date_trunc('week', now() - interval '1 week');
date_trunc
------------------------
2013-12-30 00:00:00-08
(1 row)
foodb=> select date_trunc('week', now() - interval '2 week');
date_trunc
------------------------
2014-12-22 00:00:00-08
(1 row)
I'mn using postgres 8.0.3