QUOTE(lhwj @ Sep 7 2012, 10:50 AM)
I got a third theory. The brakes is powered by engine vacuum right? If you tekan throttle until vacuum gauge points at 0, means there's
no vacuum to power your brakes 
Partially correct

When full throttle, meaning no restriction. Engine suck how much, the air filter will take how much. If your air filter so damn dirty, even full throttle your vacuum will still point at 1-2in/hg

When vacuum 0, also meaning piston draw air directly from the biggest inlet(air intake pipe) whereas brake assistent need vacumized from intake manifold. So, your theory is right. Brake assistant will not exist under full throttle(even if there is will be very limited).
Your partial right will be totally non-sense. Regardless manual/auto, you only use right foot to control brake/gas pedal. When you full throttle sprint, you don't press on brake. When emergency brake, no point hit the gas, throttle shut, gain vacuum, brake pump full force vacumized. Last but not least, when you heel & toe, what action 1st? Brake first, then clutch followed by rev up, release clutch and gas pedal

still got brake.