Calling window.moveBy(0, 0) moves the window up 22px. This seems to be the height of the window title. Calling window.moveBy(0, -22) does not move the window.
See attached test case.
Created attachment 17559 [details]
Landed in r28083. http://trac.webkit.org/projects/webkit/changeset/28083
This was a regression. It worked in Safari 3 on Leopard.