Minecarts above a cluster of minecarts will collectively freak out as the latter tries to fight its way down.

Steps to reproduce

1. Form a cluster of minecarts on a ground, either through manual placement on a rail or with a repeating command block with the command {{summon minecart ~ ~1 ~ }}and pushing them out.
2. Place a block with a rail on top next to the cluster.
3. Place a minecart on the rail and push it onto the cluster.

Expected behavior: The minecart should rest on the cluster without issue.
Actual behavior: The minecart will fight its way to the bottom, causing it and a random assortment of minecarts to freak out.