This was a problem present in 14w11b, but it seems to have resurfaced back again.

When you ride a minecart and you have some speed, once you hit a powered rail on an incline you lose all speed and stop.

Expected Result:
You should pick up speed when you hit a powered rail on an incline.

Actual Result:
When you hit the powered rail on the incline you lose all speed and end up rolling backwards.

Reproduction Rate:

100%

(Video and text from Adam)

Thank you!