Furnace minecarts doesn't seem to work anymore. Despite powering the minecart with coal and pushing on it, it just travels a few blocks before stopping (as if it wasn't being powered).

It seems the minecart is only being powered the second you put fuel into it. You can make it move forward if you keep putting coal into it, but it will slow down and stop shortly after each time you fuel it.

Coal and blaze rods have the same effect.