When a player uses an ender pearl to go into the Ender return portal on a server, the player is stuck in a sort of server lag but is not. No GUI can be opened, forcing the intervention of a server administrator to kick the player. Also, the player can't see the others. Blocks placed on entitys are placed instead of disappearing and going back in the player's inventory. I think this is a very problematic bug because on friend servers where there aren't active admins, the player cannot get unstuck.