There's a stretch of road on the west coast of Scotland called The Electric Brae (Brae is a Scots word meaning 'hill'.) An optical illusion caused by the surrounding terrain, gives the impression it's downhill when it's really up. You can sit in a car, take your foot off the brake and roll uphill. Very weird.

Not far from my house there's a downhill stretch on which I always have to pedal to maintain my speed. Coming up it the other way is always a bit easier than I would expect it to be. So, one time I tried the car experiment on it. Nothing. The car rolled downhill just like it should.

So...I can't explain the phenomenon. But I do know what you mean.