Unloading a minecart will make it sit .350 blocks higher on rail.
(Take notice of the Y value in the attached screenshots).
MC-11214
Minecarts unloading sit higher on rail
Resolved
Works As Intended
0
The coordinates are your coordinates, not the coordinates of the minecart.
When you ride the minecart, you sit (0,3 less y), when you leave it, you stand.