Fuck Lufthansa. I bought a round trip, but bought a different flight out for circumstances not pertinent to the story. Anyways, on the return trip, they wouldn't let me check-in, for a flight leaving in 2 hours, with a valid ticket through them, because I didn't take the departure flight out.
I STILL don't understand the angle there, but I learned you can buy a plane ticket to anywhere in the world (except Australia and NZ), day-of; for about $2500.