What i expected to happen was:
The command block minecart to clone the grass block and place it above it

What really happened was:
The command block minecart also cloned the rail under it.

I attached 4 screenshots. 1 being what was happening, another one showing how i'm using the kill command to help, and the 2 other screenshots are the commands of the command block minecarts
I'm also including the world download s that people can see waht's going on.