MC unresponsive when typing @ in chat

I first encountered this when attempting to type '@p' in chat. Upon typing '@', Minecraft became unresponsive to my keyboard (edit - also mouse). However, the animations and music of the game were still working. When I copy + pasted '@' in chat, however, it typed the @ character and the game continued to run as normal. When this happens I am forced to close Minecraft and the game, upon reopening, works as normal.