No useful information, go here instead: http://forums.bistudio.com/forumdisplay.php?161-ARMA-3-ALPHA-TROUBLESHOOTING

Have you actually tried firing a weapon underwater?
This isn't Battlefield/CoD.

It's the same as the shift+space feature in ACE.
When you rest an LMG on the ground, on a bipod, is doesn't go flying up into the air like it does currently. Yeah it jumps around a bit, but it won't climb savagely.