As of todays build, commanders and co-pilots that have FFV return a cargo index (AMV-4 Marshall - 0, MH-9 - 6, etc.), even though this is not a cargo position that you can move a unit in with moveInCargo (commanders still require moveInCommander and co-pilots require moveInTurret).
This causes problems with cargo detection and causes problems with units not being moved in cargo as expected.
For example, doing:
player moveInCargo [myAmv, 0];
will result in nothing happening even tho the vehicle is empty, has cargo seats and one would assume the first cargo seat in the vehicle is 0 indexed.
player moveInCargo myAmv;
Will also result in nothing happening as it tries to move the unit into cargoIndex 0 and in this case, that cargo index is taken up by the commander