Return key does not send message on IE 11

Hello everybody,
recently we upgraded our 8.7.11 Zimbra Server to ZeXtras 2.6.5 (we have Backup and Mobile modules) and we decided to move from Zimbra Free Chat to ZxChat, as suggested by ZeXtras installer. Everything works normally, but our users with Internet Explorer 11 can not send messages in chat anymore because when they hit Enter key, it inserts a new line in the chat window and it does not send the message.
Is there an option to disable this new line feature? Other browsers work normally.