The Bug
The Minecart with a Furnace can only accept Coal and Charcoal as fuel and cannot take other sources as fuel such as Planks, Lava Bucket, Dried Kelp Block etc.

Replicate

• Set a track with a Minecart with a Furnace
• Put Coal and or Charcoal in it
• Watch the Minecart go
• Put Block of Coal, Dried Kelp or other source of fuel in
• Watch it not go