Being underwater resulted in remaining stuck to the ocean's floor, walking about as per usual. During this, first person had a limited free-look FoV, the viewport was lower than the default high from the ground, and typical animations for reloading and the likes remained.
The entire period, the character was stuck auto-running, presumably Issue ID#0000125 ( http://feedback.arma3.com/view.php?id=125 )
Unclear, will list the conditions of breaching the surface of the water.
It was going down a steep hill, steep enough to provoke a walking speed instead of running.
Stance whilst breaching the water is unknown, could be related to the changing of stances whilst breaching.
Vaulting interrupted the auto-run issue, I did this once leaving the water, after remaining to auto-run after leaving the monitor.
Updating with RPT's reported version number, also found in the video, posted here for clarity.
Type: Public Alpha
Branch: Stable
Version: 0.5.102571
Issue ID#0001302 http://feedback.arma3.com/view.php?id=1302 encountered similar issue, apparently due to sprinting whilst breaching the surface of the water.
An additional video, http://www.twitch.tv/lach45/c/1995087