I know that this post is a little old but I had the same problem and tried to fix it several hours. Finally I found the solution:
if we have 2 boxes positioned absolue
<div style='left: 100px; top: 100px; position: absolute; width: 200px; height: 200px;'></div>
<div style='left: 100px; top: 100px; position: absolute; width: 200px; height: 200px;'></div>
we do expect that there will be one box on the screen. To do that we must set margin-bottom equal to -height, so doing like this:
<div style='left: 100px; top: 100px; position: absolute; width: 200px; height: 200px; margin-bottom: -200px;'></div>
<div style='left: 100px; top: 100px; position: absolute; width: 200px; height: 200px; margin-bottom: -200px;'></div>
works fine for me.