Strange Brake Problem

my car overheated one day in the city, i stopped for a few mins to let it cool down, i hit the break before taking off once i re started. pedal goes all the way down to the floor. i let the car sit a little longer, and it was all back to normal. not a problem with the brakes since.
seems our brake system is very susceptible to heat.

I would strongly suggest flushing the system. That should be done at least every two years, using DOT 4 from a new, unopened container. Don't buy huge containers of fluid, don't use old fluid, and never use silicone fluid.

Was this ever figured out? From what I've been researching, Master Cylinder issue/failure could be a possibility.