When placing Minecarts on a track going up or down or on a curve, you ride in a different position than normal.

What I expected to happen was when I'd put a minecart on a curve, you would ride regularly. Same with placing a minecart on a slanted track.

What actually happened when placing a minecart on a curve was that I was riding on the cart, I was riding unusually, because I was "leaning" on one side of the cart. When placing a minecart on a slanted track, I wasn't riding regularly, because I was sitting at a lower point than normal. Besides that, the cart itself was going below the track as if it was swimming below the tracks, with its top only exposed.