Open the testcase. Tab to focus the video element. Hit "end" to seek to the end. Hold the scrubber and drag back. The video will be playing while the scrubber is still held. When playback reaches the end of the media, the scrubber snaps to the end (despite still behind grabbed by the mouse). This is most likely a controls bug.
WFM in [Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0a1) Gecko/20120112 Firefox/12.0a1], please reopen if not.