Happens the same for me as Akheron described. The issue is definitely there on the Zeus 16+2 NATO Altis mission.
Place any unit then possess it. Cannot aim down sights.
One other issue associated with possession is if you use a unit and walk up to a body or a crate of some sort you cannot equip or move things from the crates/bodies/items to your inventory. It is as if your inventory is frozen.
Edit: Also Vanilla. I can provide video of both bugs if requested
Edit 2: It appears that since this mornings patch the aiming down sights bug is fixed. I tested it on Zeus 16+2 on Altis. The inventory thing still exists though. Will upload video in a minute
Edit 3: http://www.youtube.com/watch?v=fnCAsHXoo4A
I left in the lobby setup to show the settings I'm using for the game. Shows very clearly the inventory bug.