MacBook Air :: With Screen Tilted Back - Front Left Lifts Slightly Off Table?

I have the rev. C Air, recently bought. It works fine but I have noticed that when I tilt the screen back almost all of the way that the front left side lifts slightly off the desk. I can see that the front left pad is not touching the desk. Is this an idiosyncrasy of the computer? Do others have the same symptom? Of course once I place my hands on the computer and start typing it's not really a problem, but I can certainly feel it click down to the desk or if I lift my hands off and slightly push down there is a space there. I think it is a weight issue, because once I pull the screen slightly towards me the space disappears as well as the issue.