Peter,

what you describe is an effect which only appears near the edge of your paper sheets. It would be most helpful if you could determine whether this effect comes from the paper or from your dev kit.

A trivial way to test for this would be cutting a sheet in half before developing it and observing the edges where you cut the sheet. If the "new" edges also show this problem, you need to look at your dev. If the "new" edges are ok, obviously the paper was the source of the problem.