Super Munchkin/Half-breed Question

[ExCineribus]

I have been playing Munchkin for a while now and I've always seemed to have been confused by the super munchkin/half-breed cards. I'm usually the person to teach my friends how to play, so generally I'm the go-to guy for rules questions. The thing I can't seem to figure out is the order in which class/race cards and super munchkin/half-breed cards are played.

From the rules, the super munchkin/half-breed cards have to be played on/with a class or race. So the question is this, if you play a super munchkin/half-breed card on a class or a race card can you then play (on subsequent turns) another class or race to have two classes or races?

At this point you would obviously lose the benefits of the super munchkin/half-breed cards for having played it on only one class or race, but a strict reading of the rules would imply that instead of playing another class or race on an existing class or race that has a super munchkin or half-breed card to have two classes or races, playing a new class or race would instead replace both cards.

I have been unable to find the answer to this question on either the FAQs or the forums, and I do apologize if it has been asked before. Any clarification would be appreciated.