You can still able to bypass the LAW start up delay by air-proning and holding fire button at the same time. Once you touch the ground, it fires immediately.

Also, you can fire in air by walking off a ledge while crouching. (the delay is present tho, and you can't do this while proning and walking off a ledge.)

mmh if you have to airprone before shooting, this is a delay too. maybe its wanted like that?

I don't think it's wanted, since there also wasn't a prone-delay when shooting the LAW in the Air in Beta 3. So I guess it's a bug that remained.

Yeah, IMO, the delay should meets this conditions in order to start: 1) on the ground 2) holding the fire button 3) proning/crouching