Posted at request of Ethan...
On iOS5 devices (iPhone4S and iPad2) jwp5.8 will play the video through fine via html5 and when the video has complated the poster images and play button are displayed again.
However, if the play button is again selected to play the video a second time, the video player display turns solid black. The only way to get the player back is to refresh the webpage.
This issue exists for your own video examaple and mine (using both DIV and Video embed methods).
Ethan asked me to try the trunk player and I found a small difference. The second time the video is played there is still no response but the poster image remains.
I can confirm.
Having the exact same issues.