That happens if you make the shoutbox more than 7 lines tall. You can change the height by clicking and dragging just above the white line running above the row of buttons at the bottom of the shoutbox. It seems like it won't load more than 7 messages, so you just end up with empty space if you make it bigger than 7 lines.
Thanks. Must've done something earlier that messed it up. Fixed.
Why is this now invisible?
well, using the above click and drag method, I have shortened the height of the shoutbox in my Browser and it is all good now...