When I was on the ramp, unloading the gold you could have some fun. Before you opened up the aircraft you would ask the guard how many boxes there should be. Then you unload all except one, then start to unload the other stuff. You would see him count, then recount and then he'd call his mate over and count again. Then you'd say, oh I've found one more. You could see the look of relief on their faces straight away.
I never heard of cash going missing, but plenty of stories about gold bars. They were used as door stops etc for years and nobody knew what they were. Just a large solid object that had always held the door open.
The large cash shipments have serious security with them, you don't joke around with them.