Tamron PZD 18-270 issue using Vibration Compensation

When VC is active, my D7000 + Tamron PZD 18-270 provides usually good results. But sometimes it blurs completely the pictures. Without VC it never happens. I tested it on another D7000, and got the same results. On a D3100 results seem better. I had no chance to test another Tamron PZD 18-270 sample.

See tests here https://docs.google.com/?authuser=0#folders/0B2gAxLHqw1Y3a2cycnBxaWRHcnM (hope the link works).
DSC_5564.jpg is without VC. It can be used as a reference picture.
Other picture are with VC.
DSC_5590.jpg and DSC_5594.jpg are abnormally blurred.

I sent the lens to Tamron. They consider it as OK. They argue that my tests have no value since done with the camera lying on a stable surface. I said that I get the same kind of results in my hands... In the meantime my lens is by Tamron waiting for new tests.

Did someone experience the same with that (or another) lens? How did you solve the issue?

Thanks,
Fred