This bug causes completely empty divs to have a minimum height of 20px
The code contains something like this: <div></div>
You will only witness the bug in IE6. The photo to the right shows what it looks like.
The red div is set to 5px high, but displays 20px high in IE6, even though it is completely empty
The blue div is exactly the same, except it contains a comment inside the div "<!-- IE Sucks -->".
That is enough to squash the bug
The green div contains an empty paragraph inside an empty div. That squashes the bug too.