The bug:
End crystals don't place right before you left click. Not very good if you wanna place and break crystals as fast as possible in crystal pvp.
Steps to reproduce:
1. Place an obsidian and a crystal on it
2. While holding your crystals, break and try to place immediately
Never mind, it happens on servers but not in singleplayer even if you have low latency. Probably because of the server lag.