As I said in an earlier post, I too am having slight trouble with the smart cover over the icarbons skin.
Now, I don't believe that the problem is that the skin itself weakens the strength of the magnets. What you'll notice when you put the smart cover on, is that the film only extends about halfway under the hinge. What I think this does is create an uneven surface for the smart cover to adhere to, and because of this, allows the cover to slip up and down, left and right.
To demonstrate, put your smart cover on, fold it into the triangular stand, and (Being careful not to drop the ipad) place a slight bit of downward pressure on the cover. You'll find it slips and loses adhesion every time.
The simple solution would be to trace the outline of the hing onto the right side of the cover (as it lays on the sheet) before you apply it, and cut it out using an hobby knife. As for those of us who have already installed the skin, I have no idea how you would go about removing the material without damaging the ipad underneath. The only solution would seem to be to remove it, order a second skin, and modify it.