IE6 negative margin issue

[sKunKbad]

In the following code, the yellow box should be 100px tall, half on top of the white box, and half on top of the green box. IE7, Firefox, Opera, and Safari display this fine, but IE6 cuts the top half of the yellow box off. Any help is appreciated.

 

<div style="float:left; width:100%; height:100px; border: solid red 1px;">Box 1</div>
<div style="float:left; width:50%; height:100px; border: solid black 1px; background-color:green;">
<div style="float:left; width:50%; height:100px; border: solid black 1px; background-color:yellow; margin-top:-50px;">Box 2</div>
</div>