[unfasten]

This does not seem to be encouraged behaviour.

via http://support.humblebundle.com/customer/portal/articles/243...

        If I already have a game(s) in the bundle do I have the ability to
    gift the extra copy in the bundle?

    Unfortunately, if you already have a game in the bundle you will
    not be able to gift the extra games to a friend.

    Please consider your bundle a "unit", and not to share copies of the
    games or Steam keys from it.

    If you'd like to give a copy of the games away, we have a system in
    place that allows you to buy a gift key from www.humblebundle.com so
    your friends can have access to direct downloads as well as any Steam
    or other keys we have included.

[ihuman]

Then how come they are separate? If they want to discourage people from giving away the games as a non-unit, shouldn't they make it one code like they used to?

[EvilLook]

It's probably harder to create a "unit bundle" key with Valve for Steam if you're only going to sell this bundle once and never in the future. You don't need any coordination with Valve to give away Steam keys. You only need coordination with the game developer.