Text Area Problems…

I run a blog/resource/tutorials site. I noticed that when I put codes in the Textarea boxes this <p> keeps showing up at the end of the HTML, Which messes up the whole code! Is there a way to fix this? I already tried plugins they didn’t work! If you need an example here’s one:
http://midnight-desires.net/tutorials/css/custom-bullet-list
Look at the end of the last text area box.