To reproduce: 1. Go to any web page 2. Resize the Safari window so that it has a horizontal scroll bar 3. Hold down the Shift key and scroll the mousewheel vertically Rolling the mousewheel up scrolls to the right, and rolling down scrolls to the left. It should be the other way around.
<rdar://problem/6310511>
This ended up getting fixed in r41507 along with bug 24405. *** This bug has been marked as a duplicate of bug 24405 ***