If you have a definition list  in a relatively positioned div tag, the background image may disappear in Internet Explorer.

The solution is simple. Add a width declaration for the element in your style sheet, i.e. width : 100%;

If this does not help, you can try this tip from  Matt Smith at http://www.positioniseverything.net/explorer/ie-listbug.html:

Add the following declaration in your style sheet: 

ul, ol, dl {
     position: relative; 
}