What I expected to happen:
The minecart will turn when it arrives at the turn in my rail.

What actually happened:
The minecart will stop and return to where it started.

Steps to reproduce:
1. Create a world and type "/gamerule doMobSpawning false" into the chat.
2. Get yourself rails and a minecart, simply have a turn and push the minecart towards the turn.

Additional Information:
I was confused and tried creating a new world and it worked perfectly fine, nothing wrong with the turning. So I returned to my original world and tried it on different blocks, still nothing helped. Then I remembered I had set doMobSpawning to false. I set it to true and it went back to turning normally.