In some rare cases, it seems like packets are either sent to the server out of order or recieved out of order, which doesn't seem to make any sense, given that Minecraft uses TCP for it's game connections.

We've tested this and managed to have the server receive a packet for damaging an entity on the server before it received a packet from the player closing their inventory, which given the flow of the game makes no sense - since players can't hit entities until after they close their inventory (modified clients barred here).

Based on this, the server should be receiving the inventory close packet before any packet about the player hitting an entity, however this has proven to not be the case with players with high ping/unstable connections (such as players from Australia to the US).

I'm not sure if this a large bug or just some obscure race condition, but either way, the packets shouldn't be ending up at the server in the wrong order, since that could potentially cause some eventual issues.