Signs crash the world/ Planting Cocoa beans kicks player

I attempted to place a sign on a multiplayer world, but we were unable to stay in game. As soon as the sign is rendered, it kicks the player. Host said something about 'millions of duplicates'

Also, when attempting to place cocoa beans on a jungle log, the player planting them has their game crash. The cocoa beans do not stay planted after restarting the game.