User types in chat, everyone gets disconnects and then receives a JSON error.
http://i.imgur.com/2XEb1dd.png
The "." is the text that was inputted. Any text you will be kicked.
This also goes for any command.
/gamemode
/give
Tested on two servers and receive the same result.
However, chat works fine in Singleplayer.
Environment
Server is Linux x64 and Client is on Windows
Fixed for a future version. MC-85837