Sarah, Personally, I think it's a variance in the adapter itself. It's really easy to bend the pins in those things if you're not careful. I think that sometimes they will still make just enough contact to work, but that contact may not really be solid enough for good results with something like a wireless card which does draw significant power. If that power happens to be down a little, it may still work, but the signal strength could be less and therefore not as reliable.
So, I'm really careful when putting a card into the adapter I'm using. I've actually lost a couple of adapters because of bent pins internally caused by accidently putting the card in incorrectly. Don
