A munchkin is someone who follows the letter of the rules of a game while breaking their spirit, someone who wins by exploiting possibilities that others don't see, reject as impossible or unsporting, or just don't believe can possibly work.
If you have done something that everyone around you thought would not work, something that people around you didn't do after they saw it work, please share your experiences. If you tried something and failed or have ideas you want to hear critique of, likewise please share those with us.
I think that's true in British English but not in American English. (I am a native BrE speaker and lots of AmE participles look wrong to me for want of a doubled letter.) Since the Munchkins are the creation of an American author, I'm quite content with the spelling used here :-).
Oddly enough, I'm a native speaker of American English. Maybe I'm just weird. :)