Experience orb position client-server desync

Experience orbs sometimes keep swirling around you, without ever being absorbed no matter how long you wait. This is because the client and server disagree on where they are.

In a recent Minecraft version, more sync event have been added, so now the orbs are jumping back to where the server think the orbs are about once every second or so. But it is still obvious that they are buggy. One specific issue is half-slabs, which the client thinks the orbs can climb over, while the server disagrees (this might or might not be the only problem).

Video demo: http://youtu.be/oVwu3LOgS14