in the snapshot 14w11b powered rails dont always work on slopes

Put the summary of the bug you're having here
I was testing the new minecart speeds, I put about 6 powered rails on some redstone blocks in a diagonal upward slope. first I pushed a regular minecart, as expexted it went shooting off. but when a player or a mob, in my case a sheep go into the cart and try going up a slope on powered rails, you get immediately shoved back down as soon as you hit the slope
What I expected to happen was...:
I expected to see the sheep go across the track and shoot off the end

What actually happened was...:
, after about 5 tries you usually get up the slope, but you don't always fall off in the same spot when the minecart falls off the rail
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...make a simple diagonal slope with powered rails only, with a small runway. about 8 blocks leading to the slope.
3. ...get into the minecart and shoot off, the minecart will bounce back as if it hit a wall