This page runs a SHA-512 (Jeff Mott's CryptoJS implementation v3.0.2) on the input string that contains 12 \x36 characters. It does so 100 times and complains if the results don't align. If it finds a disagreement, it will output the attempts that didn't match (when compared to the 0th attempt which always comes out correctly).
This page gives me unstable results on Chrome 25.0.1364.99 on Mac OS X 10.8.2. Reload a few times to see what I mean.
It works as expected on recent versions of Sarafi and Firefox (and older versions of Chrome).