Seems like items are disappearing before the 5 minute mark if no one is in the area. Died in an area, and used mod command to go back, and the items were gone. This happened a few times. Tried re-logging and still were gone. Same with paintings. D0rk tried it to confirm, same thing with him. May need to be cautious with death, items will not be there when you get back.
Yeah, what happens is, as you know, when nobody is in an area, reeds don't grow, same thing here, if you're not in an area, items will disappear, but unlike the reeds, this isn't supposed to happen, question is, is it minecraft? or a plugin, I'm thinking it's a plugin because it didn't do this when we updated to 1.6.6.