That is odd. Do you have a failsafe (or Spektrum) that is set to brake when the radio loses signal? But then again, the receiver pack should have cured that. I didn't think the MM went full brake when it "rebooted".
Nope, no failsafe. I mean two different cars, two different servos, three different motors, two different esc's, two different radios(both FM), and two different receivers and the problem persists with the 3s not the 2s. So, the only thing it could be is the battery.