null. Behavior is not defined if more than one element has this id. Parameters: elementId of type DOMString
This bug has been reported at connect's IE beta feedback as bug 333979 and has also been reported at Web Bug Track bug 152: getElementById returns incorrect objects in IE.
Update: This bug has been FIXED in Internet Explorer 8 beta 2 (build 6001.18241) released on August 28th 2008. Otherwise, Internet Explorer 8 beta 2 PASSES this specific and particular testcase.