Weird Brake Problem

[ProTouring442]

OK guys, here's the deal...

The Car: 1959 Chevrolet Impala

Front Brake calipers: '69-'72 GM A/F body (2-3/4" piston)

Rear brake cylinders: '59 Impala (1" bore)

Master-cylinder: GM 1-1/8 bore disc/drum

Combination valve: '69-'72 GM Intermediate

Power booster: Astrovan hydroboost

All new lines and flex hoses

The car stops great. It stops well with all four crying. But, if you press super-hard on the brakes while at a stop, you can make the brake light come on.

At first I thought it was a master-cylinder... replaced it. It's not.

Went ahead and replaced the combo-valve. That wasn't it.

I have bled the thing absolutely to death.

What am I missing?

Thanks!!!!!!!!