Strange behavior in sortable on Safari
If you create and make your window small enough that the user needs to
scroll to the item list they want to sort the item is offset from the
cursor the scrollLeft and scrollRight amount.
You can see this by going to your Sortable Massive Scale Test and
scrolling down to an item lower on the page. When you drag it, it
will be offset from your cursor by what appears to be
document.body.scrollLeft/scrollRight distance.
I have a patch that corrects this on Safari and still works on firefox
if anyone is interested.