I'm pretty much having the same problem. Clicked the "Buy this pack" button, typed in the email that i wanted to use, clicked the "Checkout" button, then realized that I probably want to make an account first just to be sure I have one and whatnot and proceeded to close the little pop-up window. When trying to make an account after this, I too got the "Email already in use" even though it really isn't. Going through the "Forgot password" process then does nothing, no email get's sent to me, there's no account linked to that email, it just seems to be remembered by the server's or something. Quite annoying.
Hopefully this is something you'd be able to fix as I don't want my purchase to be linked to a secondary email (like the account I'm using now).