What I expected to happen was...:
The minecart with hopper to dispense onto the rails.

What actually happened was...:
It was dispensed like a ordinary item/block.

Steps to Reproduce:
1. Place a dispenser and put a Minecart with hopper in it.
2. Place rails in front of the dispenser.
3. Activate the dispenser with redstone.
4. The minecart with hopper will be dispensed as a item not onto the rails.