Any strange issues with items not publishing when expiring in the afternoon?

One of our blog admins is unable to publish items when they are scheduled to expire in the afternoon. For example, an item wouldn’t post if he set it to expire at 13:00:00 but the same item posted fine when he set it to 08:00:00. I have not encountered this problem and am able to publish all my items just fine. Any idea what might be causing this anomaly?

http://wordpress.org/plugins/content-scheduler/