I have been unable to replicate the problem you report (on a PC).
I have viewed the demo gallery in Firefox 28.0, Chrome 34, IE11, Safari 5.1.7 and Opera 20.0 and after expanding and closing the gallery, AutoPlay does not automatically start.

I do not know what might be causing the problem on your own system but try clearing your browser's cache before reloading the gallery to see if this makes any difference.

In the meantime, I have notified the developers who will be able to try it using Safari 7.0.3 on a Mac (the same setup as yourself) to see if the problem can be reproduced.

It doesn't happen every single time, but most of the time. I'd say 9 of 10 times.

I've recorded my screen to show you what is happening:
(before the video I've cleared browser's cache, as you suggested)
https://www.youtube.com/watch?v=_eerg9k … e=youtu.be

Please notice strange thing that happens:
1. After first Expand Mode and Exit, Autoplay icon blinks. It changes to Pause and Play (I didn't hit any key).
2. After second Expand Mode it blinks one time more. Changes to Pause, then Play and then Pause again, so Autoplay has started this time.
3. After third time with Expand Mode, the icon blinks one more time again. Pause->Play->Pause->Play, so the Autoplay stays off.
4. And so on...

Weird pattern, right? It seems like each time when turning off the Expanded Mode, there is this one extra Autoplay button hit.

Latest Chrome acts almost the same. The difference is that this blinking is not that noticeable. But it also switches on the Autoplay button.
I think it is maybe because both these browsers come from the same WebKit engine.

As I have said earlier, there isn't a problem with latest Firefox.

Great.

Just a side note: I think it is clear on the video, but if not... The problem is only with the Fullscreen Mode. When I use Expand Mode to only expand to browser's window, there are no problems at all. Every browser works fine then.