KneeTheCap: So the only way to see if the keys still work is to get someone to redeem them and check it out. Convenient...
Thats just how Steam works though and always has as far as I know. Its not anything to do with Humble Bundle or any other place where you can buy Steam keys. When you have a Steam key, the only way to know for sure if its been used is to use it. It will either tell you its a duplicate or it will activate it for you.
I suppose the 3rd option is if you already have the game, and the key has not been used. I don't know what it tells you then. Hopefully the game won't start installing and waste a key for you that way.
And I've heard legends and rumors that if you contact Steam support to ask if a key is active or used, they will tell you. But from those who recite these tales, they say it is a long and arduous journey fraught with the unknown of whether or not you shall find your answer and thus your salvation. (um, in other words, support will take forever to get back to you).