Tamron 70-300mm F/4-5.6 Di VC broken?

I have a purchased new Tamron 70-300mm F/4-5.6 Di VC. I love the lens except for one thing. With VC active on my D90, I can have the focus point on let's say a persons's eye (my right side) but when I depress the shot button half-way the focus appears to get made but then the focus point shifts left, about to between the eyes. I do not have this problem with any other lens nor does this lens do this w/o VC.

Anybody else seen this? Bad lens? Definitely aggravating.
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Colonel Blip