Closed and restarted your browser? Did you try refreshing the page first?

I know of one problem with the JavaScript like this, but it's cured by reloading the page. After getting comfirmation from the server that the comment was received, the script creates a new entry in the comment tree with its title, but it's not able reconnect the script that lets you download the comment body and read it (it doesn't know the ID of the newly-created comment). That won't happen until you refresh the page and get the "official" copy of the updated comment tree from the server.

If you experience the problem again, could you take note of your actions, refreshing the page versus restarting the browser?