I think that the problem is caused by the absolute positioning of your text areas. I've come across this before and haven't found a cure without re-writing the whole site using different techniques.
A work around would be to create a footer style and insert it in a div immediately in front of the closing div for 'maintextarea'. Try:
margin: 0px -5px -5px -5px;
Insert into your page with '<div id="footer">Copyright text</div>'