The play/pause button in the full-screen video controller does not reflect the current playing/paused state of the video. It seems to always come up as a Play button when going into full screen, regardless of whether the video is already playing. When the video reaches its end and stops, the button doesn’t change. Clicking the button always changes it.
<rdar://problem/7297717>
http://trac.webkit.org/changeset/49948