Right, that's the problem, so the publish_date is 2012-05-02 00:00:00 which is *less* than the request creation date of, say, 2012-05-02 18:38:00.
The sweeper query requires that the request creation_date <= notif_date which in this case is the publish date down to the day. See notification/tcl/sweep-procs-postgresql.xql
The same issue appears when the subset feature is used since the request is created ms after the item.