The bug causes a desync between the server and client. At first the player gets disconected, but everone else on the server still can see the player on the tab list and his player model. When the player reconnects, he can see his own player model standing a couple blocks away. After ~30 seconds the chat shows that the player disconnected, but he still is in game. In this state the player can interact with all blocks and entities, including killing entities and destroying blocks. When the player relogs, he is back to normal. I'm also pretty sure the player model is visible in this state too. I made this post private, because there is a way to toggle this bug. I don't know it, but we had a griefer on our server who exploited it to destroy our world. I only had this bug twice, so I couldn't experiment with it a lot. It happened in versions 14w27+