Defective 70-300 VR or normal behavior

Just got my new airshow lens, 70-300 VR, and it seemed to work at first. After about 2 days it seemed to start focusing about 2 feet behind each subject in the center of the scene. Have others seen this behavior with this lens?

I sent it back to B&H for exchange. Tried it on D70 and D80 bodies with same result.