If the HTML element has a -webkit-transform property, the mouse events need to take this into account when calculating the pageX / pageY coordinates.
Please also see https://bugs.webkit.org/show_bug.cgi?id=67592
Why is the HTML element special? I don't think a transform on the HTML element should affect pageX/pageY.
Simon, I think that makes sense to me. If I understand correctly, we can mark this bug as invalid: A css transform on the HTML element is no different to a css transform on any other content element, for example a <div>. We wouldn't expect a css transform on a <div> to affect the PageX and PageY mouse coordinates, and similarly the html element is no exception. A transform on the HTML element changes the coordinates of the top left corner of the HTML element, but not the document itself. PageX and PageY coordinates are relative to the top-left corner of the document.
Sounds good.