Hello.

  I'm afraid that there are some issues related to Minecart hitboxes, with the Hopper Minecraft giving me trouble, specifically.

 When two carts are in separate tracks but said tracks are in a direct diagonal (ie. if track 1 starts at 0,64,0 track 2 should start at 1,65,0), the minecart on the upper track can transfer items to the one on the track below, even though they don't actually touch (and shouldn't be able to).

  Another minor bug is that when in a North-South facing track, normal minecarts prioritize facing their rider North instead of ignoring the direction the rider was originally facing.

 Since it's just a small problem with the collision box and some behaviour it shouldn't be too troublesome to patch.