Intermittent no rear brakes?

[Bohnzye]

Alright you wrench heads< said affectionately..As the riding season nears end...((Here in Ohio, I have a loss of pedal on the rear caliper. I have bled and re bled the rear master cylinder at which point it's fine and then when I ride the bike I loose pedal completely until I pump it up coming to a stop. No loss of fluid or leaks. Really miffed here.. Take a number...zzzz Thanks fellas

 

[Vicman]

Is there excessive run out on the rotor? Easy to check, put it on the center stand and set up a dial indicator. Is there any play in the rear wheel?
I suspect there is play in the wheel or the rotor is warped causing the pads to bump back into the caliper a little further than you get from a normal press on the pedal to stop.