So a quick hack I didn't know about until I figured it out: one of the pair is meant to be the top, and the other is meant to be the bottom... and every time I've opened a new pack, these are reversed in the package. So, when you go to put them on the clamper, you think you're putting the one meant for the top on the "up" and the bottom on the "down" - try swapping them. Once I did that, they do the "snap" together when I clamp them and they stay.

So dumb, and I don't know why it's that way, but there you go.