[shorod]

Sounds to me like the brake line wasn't connected properly or was cross-threaded. When the power assist was working, the pressure built up by the brake booster forced the line off and put a whole bunch of air in the system. I'm guessing you didn't get all the air out of the system since you don't have leaks currently. You may also want to remove the brake line and closely inspect the threads for signs of prior cross-threading. You don't want the line to pop off while panic stopping on the highway.

Was the master cylinder off for any reason recently?

-Rod