Background image disapears in IE

[IncaWarrior]

In my page (http://strategyplanet.com/populous/) the center of the page has two divs ("main" and "inmain" to give both sides of the page a border. For some reason the top sections of the backgrounds disapear in irregular sections in IE only. Here's the CSS:

div.main{ /* Outer Box For content */
     background-image: url("images/mainL.gif");
    background-repeat: repeat-y;
    margin-left: 160px;
    margin-right: 20px;}
div.inmain{ /* Content */
    background-image: url("images/mainR.gif");
    background-repeat: repeat-y;
    background-position:right;
    padding: 0px 9px;
    margin: -10px 0px;} 

[IncaWarrior]

I've narrowed it down now so I know what causes it. For seom reason the negative margin on the inner div is what causes it, when it's not there the background shows up.

Knowing that I can just use an IE hack