I recently found a strange webkit bug when I used a negative top margin to position a floated element.
I float an element to the left and gives the outer wrapper element a top margin of ex. 100px. Then I give the inner child wrapper a negative margin-top of 100px to push the floated element down. In most modern browsers this works, but in Chrome and Safari we can see a hole where the floated element would have been without the negative margins. The floated element further down looks fine.
[example] (test with a webkit browser)
The “fix” is a strange one. I insert an empty floated div before the inner child wrapper and the phantom float disappears.