The W3 offsetParent algorithm changed on 9/15. It now includes ancestor elements with a CSS transform applied. Chrome and (maybe?) FF are in compliance with the new spec, while IE and Safari are not. As a result .position() is now returning incorrect results in these browsers.

IMO jQuery will probably need to implement its own ancestor traversal rather than relying on DOM-provided .offsetParent, otherwise results will forever depend on the browser+version of the client.

See: w3c/csswg-drafts#409