18-200 VR - Inconsistent VR?

Hi all. I just got the 18-200 VR and have been noticing an issue.

Occasionally (like maybe once per 4 shots) the VR simply won't "lock" like it should, and the lens continues to wobble normally, as if the VR isn't doing anything.

When that happens, I'll press the shutter-release down halfway over and over and over, and it will not "lock" until after I take a picture.

Fortunately, I've noticed that most of these shots still come out okay, but then again, SOME shots that seemed locked come out totally blurred.

Does anyone else notice this? Could this be a defective lens?

Thanks.