Thanks for the note on that -- I've just sent a query over to Valve about it, and I'll let you know what they say. I see that it works to buy just the single copy of the game as a gift if you already have it, but the bundle works as you describe for me also. Thanks for the catch!
EDIT: Ninja'd by Keith. Yeah, I thought we had spoken to them about that before, but I couldn't remember for sure and couldn't find it in my email history. Well, I've sent them another note about it to plant the bug in their ear one more time, anyhow.