Those frickin' nuts always loosen up at some point. I can really only think of two reasons why they exist. 1) To pull the valve up into the hole as much as possible but you don't need this if you know how to inflate a tire from 0. 2) To keep the stem centered in the hole. Well, install the tube properly with the stem centered up to begin with. The tube doesn't move around if kept inflated properly.

I've also heard of people tightening the things till the valve stem patch rips. Just toss the thing at Knotted.