[Nukapei]

This has confused me as well, and the explanation I came up with was similar. But, important is the fact that Sauron taught the Elves how to make their Rings! Maybe he knew they'd try to make their own, maybe he didn't. I haven't read that many passages on this subject -- most of my knowledge is second-hand. However, it seems to me that, even while he was teaching the Elves this craft, he would know that there was at least the possibilty one of them would do something like this. And, call Sauron a lot of things, but dumb he ain't. If this thougth had crossed his mind, he probably would've done something about it. So, it's possible that he might, might, have taught the Elves to make Rings of Power a specific way, with a fall-safe installed that anything they made using his methods would automatically be tied into any Master Ring(s) he might make in the future. Just a thought!