This occurs nearly every time I attempt this in the Warlords mode on the Official Warlords multiplayer servers.
Essentially , when you obtain a vehicle, and have an AI squad- once you load up into a vehicle with them and then open your map and command them to drive somewhere, they WILL NOT do so. They typically will refuse as long as you are in the vehicle. In the past, they did not exhibit this behavior.
Something to note: In the times in the past this did work - when you ordered them to move somewhere, they would take a second, then suddenly start following orders - like it takes a second for some sort of logic to be triggered before they will take action while you are in a vehicle and they are as well(and yes, while they are in the driver position, obviously.)