So last night during a KSPTV stream one of the guys had an elliptical orbit around a planet and while close to his perigee he couldn't exit to space center because his craft was accelerating... he also noticed his apogee was rising so something was causing his craft to accelerate while close to the planet. I am also experiencing this now, I have a probe on a polar elliptical orbit around Jool (230,000M x 1,300,000,000M) and when I get near the perigee my craft starts accelerating and my apogee rises. Something is causing acceleration.