You can fix that by setting the "Word cutter" setting in your adminpanel to a lower value. I think its standard at 18, which cuts words after the 18th character. Setting this to a lower value may prevent this. You should set this value according to the width of your shoutbox.
If you have a wide shoutbox, you can set a higher value, since more characters can be posted before it becomes too wide for the box, and it goes the other way around if you have a small box.
