At random times on my server, I can't pick up dropped items, even though my inventory is NOT full! I also couldn't place blocks; they would be placed for a moment then disappear and be back in my hotbar. I also can't push buttons.
Disconnecting and reconnecting fixed it, but I would be in the spot that I was in when these problems started.
This happened twice over the past few days (on two separate days). I didn't happen before I updated the server to 1.5.2.