Very often when I try to draw a vehicle from the deploy screen I just get spawned in as a troop with no vehicle and still have to run to the pad. The first time I thought I must have screwed up, but it keeps happening. So: No, it's not operator error No, the pad isn't hacked No, the pad isn't destroyed.
Follow up: It seems like I have to wait until the spawn timer ticks down for the feature to be available. If I select what vehicle I want and then wait for the seconds to tick down I'll get spawned in as infantry despite having selected a vehicle.