Master cylinders can develop a problem where the rubber cups leak past internally. They won't leak, outwardly, and depending on how bad the problem is, the master may "stop" the car OK, or not, and may slowly, or quickly leak towards the floor. Sometimes "stomping" the pedal quickly will "seal" the cup temporarily, while often "easing on" the brake will cause it to leak right down.
That's kind of what happens. If I stomp the pedal fast enough, I get a little braking action. But depressing the pedal at a normal rate, it goes right to the floor and the engine pulls the car along with zero braking.
I've found a couple threads where they talk about what you describe; I'll keep digging. I'm also now wondering how difficult it would be to rebuild my master cylinder, or if I should just buy a new one (if that's what the problem is).
