The pixel test is correct, but if you run the test in Safari and change the system preferences to always show the scrollbars, you don't see the scrollbars moving.
I contacted the author of the test and she confirmed that the scrollbars should be moving when running this in the browser.
The test does not fail in WebKit2. It looks like it is a WebKit1 only issue.
It seems to work just fine on Mountain Lion at least.
Still failing on WK2 bots.