The Reply dialogue no longer works after WP 3.9 upgrade. After selecting reply, it takes you to the correct page, and fills in the appropriate message, however, the input box for the message is un-clickable. And switching from Visual to Text mode and back and forth does not resolve.
After choosing "Send" which shouldn't even be allowed as the "Message" is a required field I get a status message saying my message has been sent. NOW, the message box is editable and I'm able to enter my message and successfully send the message.