It seems that I'm the only one here that needs more to go on than just a "feeling" to diagnose a possibly non-existent problem.
BTW, I just checked and mine has the same "feel" on the brake pedal with engine off as the OP! Start the engine and it "feels" normal again.

What does 4700k mean?

 

Well then maybe you have a problem as well! The braking system vacuum should not bleed over time.
4700 "miles on the odometer"

 

Pardon my confusion but a "k" following a number usually represents thousands which would be 4.7 million miles.
Taking the car to the dealer is such a hassle that without any symptoms of a problem while driving would be a waste of time. They're just going to tell you it's normal.