While diving with the mouthpiece it never tried to close on it's own even with a good amount of surge and water movement. There is also a 3rd O-ring that I don't have on it that was designed to cause friction and insure positive open or closed position. I don't have it on the sample as it was not necessary.
I was opening it all the way in the video...I think it looks a little different because the sample material has reacted to the O-ring and lubricant and left residue on the clear material. The production will be made from ABS and this wont' happen.