CSS and span tag MouseOver issue

[jpollock]

Is this a bug in IE7?

When you use CSS and a <span> tag for a mouse over thumbnail effect IE 7 renders in a different location.

When you hover over the thumbnail in IE 7 compared to IE 8, the IE 7 version renders the span higher on the page then the IE 8 version does.
IE8, Firefox, Chrome and Safari all render the span tag in the correct location. IE 7 dose not.
CSS code:

.thumbnail span div
{
position: absolute; background-color: transparent; padding: 5px; top: -260px; left: 0px; visibility: hidden; text-decoration: none;
font-family:Arial; color: white ; font-weight: bold; font-size: 14px; text-indent: 25px; z-index: 1000;
}

.thumbnail span img
{ /*CSS for enlarged image*/
border-width: 0; padding: 50px 50px 50px 50px; width: 280px; height: 280px; z-index:6000; z-index:1;
}

.thumbnail:hover span
{ /*CSS for enlarged image on hover*/
visibility: visible; top: 30; left: 160px; width: 380px; height: 371px; z-index: 1000;
background:url('../images/frame_lg.png') repeat scroll 0 0 transparent;
/*position where enlarged image should offset horizontally */
}
.thumbnail:hover span div
{
visibility: visible; top: 0; left: 0px;
}


Has anyone see this or have a solution?
Thanks for your time