I don't know if this is intentional or not, but when attempting to quickly type multiple messages in battle, one after the other.
Ie.
Enter (Start typing)
<Message>
Enter (Send message)
Enter (Start typing)
<Message>
Enter (Send message)
There is a lengthy period of time (very annoyingly so) after I send the first message where pressing Enter does nothing. Really frustrating when trying to give quick directions or instructions to a coop partner.