Ah, that works, but it is not in the Chatterbox FAQ.

The only reference to the talk button is:
All you have to do is type a message into the Chatterbox text box and click "Talk".

To me that implies talk is only used for sending messages. Now that I know it will not submit an empty message I can refresh the box without being annoying.

I propose making adding "To refresh the chatterbox simply click on the Talk button when the text entry box is empty." Or somesuch.