OK ... This is not really a bug, but a lag which occurs after the generation ...
If I can help you, the problem appears in typing : copy / paste text with special characters (like É) works, the packet sending / receiving works too. This is when the keys are typped that the problem appears.
The bug wasn't fixed in 1.8.4, we can do a @ in the chat, but any alt combinaisons. Also, we can't use the Alt+Gr in commands.
Confirmed in 15w47c