Odd but true. What you're describing is about what happened to me. Low pedal after bleeding but OK once I drove it. Really can't explain it. I had an ABS warning light on the dash when I started it after bleeding the brakes without the booster. I think, though, that I had turned the key to RUN during my axle swap job, and had the two front sensors unplugged at that point. So I don't think the ABS light and the low pedal were ever related.
HEY, in case you didn't see it on another thread, we should be changing the Power Steering fluid as well as the Brake Fluid. An OP with a Chevy P30, same booster concept, had a sticking brake pedal and it turned out to be gunk in the power steering fluid. Changed/flushed the steering and was back to OK. We've had a case on the Class C forum of power steering fluid getting into the master cylinder at the booster, so again, good idea to refresh the fluid on both sides.