Today, i reproduced if a minecart can ride a boat, my conclusion was the minecart ride the boat BUT you can't ride the boat or the minecart. For resolve the problem, you need to cut the boat.

Step to reproduce :

1. Place a boat and a minecart.
2. Collide the minecart with the boat.
3. When the minecart riding the boat, click on the boat or the minecart.