I don't think that is by design. But upon further reflection we feel that the dull side may have a tendency to stick a little less.
We also have fallen in love with the "Release" version for placing under delicate foods.
For salmon, rub it w/ fat of choice then plop down the fish. Season as you wish and grill alittle past opaque. It almost slides itself off of the foil.
I've done this with and without cutting slits in the foil. With slits results in a cripser skin, but it seems to make the mudline (dark meat along the lineal line) taste a little stronger, but not oblectionable