Yep. I'm sure I'll have to make this point again, but it is indeed as JC says. A random list of ALL your objects, not just one of each type of object you have, is made. Then however many you're tithed is taken off the top.
I've also asked this and got the same response. It seems it would only be a 1 in 41 chance.
You probably are inclined to think your most valubles are most likely to go, because you remember when they do! As in, if the 1 in 41 chance happened, you're going to think, "Oh, the evil bastard stole my ICBM!" whereas if he takes a Coal, you're unlikely to remember it.