I have a relatively new home brick veneer and I am getting cracks in the brick work randomly around the house. It appears as though the mortar has shrunk and has not stuck to the brick work. I have never seen anything like it before. I am confident it is not related to foundation movement as they are predominantly horizontal and all around the house.
Sounds like you are thinking in the right direction. There are really two posibilities for the excessive mortar shrinkage. It could have been mixed with too much water,causing excessive shrinkage when it dried, or the bricks could have been exessively dry and sucked the water out of the mortar before it could cure properly. As for the mortar not sticking to the brick, that is usually an indication of a mix that contains too much sand.