[simplechamp]

If I remember right the stock punch control setting on the MMP is 0% (disabled) so you might be overtaxing the batteries when you hammer on the throttle, the pack voltages drop and the BEC shuts down momentarily. With the capacitor added it might be just enough to keep the system alive until the pack voltages stabilize and rise back up. So maybe try adding some punch control and remove the cap and test again. I could be totally off-base, but it seems possible to me.