It's possible that this is functioning as intended by BI, but I cannot access my inventory, or the inventory of dead enemy soldiers while underwater. I believe this needs to be changed, as it is perfectly possible to dig around in a rucksack or remove something from a pouch while you are in the water in real life.
My specific concern is the way this could effect multiplayer. Imagine you and a friend are playing a mission where you have to swim ashore at night and plant satchel charges on enemy helicopters. Your buddy is the one carrying the explosives, and a sentry spots and shoots him while you are both still in the water. The way things are now, you can't recover the explosives from his corpse, and thus you fail the mission. An experience like that would be needlessly frustrating and immersion breaking for the players.