When furnace minecarts are used to push other minecarts (even empty) they lose all momentum and slow to a crawl.

What I expected to happen was...:
I expect them to go faster, and push the minecarts with more speed.

What actually happened was...:
They stop and get jittery

Steps to Reproduce:
1. Make a track with normal rails on flat ground
2. make a furnace minecart go fast on it
3. place down a minecart in front of it

4. Optional: decrease speed to 2, and you see the normal minecart start acting strange when the furnace cart approaches.