Put the summary of the bug you're having here:

What I expected to happen was the Minecart to go higher than y=33.

*What actually happened was the Minecart stopped and went back down when I wanted it to go up

Steps to Reproduce:
1. Go to y=32
2. Place a minecart on a rail/powered rail. Doesn't matter.
3. Try and make the Minecart get to y=34.

This bug happens in both creative and survival. Also, it's happening to me in build 6, but will only let me go up to build 5.