The received accuracy is against the squad, not the actual weapon they are manning. If PTRS's take out the squad of the weapon, and it's legitimate, so be it. For the weapon itself to be destroyed (so quickly) like it is has been shown to do, is a bug, I am certain.
As for your second part, it's no different than any other blob in the game, whether it contains Obers/Grens/Rifles or Cons. That is a game wide issue, not only related to cons.
i strongly doubt it's a bug. PTRS probably can't miss against the weapon (they can't against vehicles afaik) and they target it instead of the crew. might be fixable by changing the target priorities of the PTRS to infantry but idk if that would screw with vehicles or not.