nchawkeye took the right approach there, check the mounting screws on the base and the scope rings.Like him, I will not mention why this is important...

As for why it would move like that, I have seen the same thing with a Bushnell I had. I called them, and asked them what was going on. They asked I send it back and when it was returned, I would not swear to it, but I am still under the impression they gave me a new scope for the old one. Their note said, they could find no problem. I remounted it and they were right, there was no problem. What they did, I have no idea.