Minecarts won't roll on curved rails

What I expected to happen was...:

the minecart, as always, should roll with ease across all rails.

What actually happened was...:

it stops, and goes back, as if it hit an entity or mob.

Steps to Reproduce:
1. get a minecart
2. make a line of rails
3. add a curved one at the end
4. let it roll
5. for me, every single time, it comes back as if it hit something and rolls backwards.