B+W Coated Circular Polarizer filter
That does not sound right at all. I would immediately send it back for a replacement. The surface should be perfectly even. Surprised to hear this about a B+W filter.
For what it is worth, I use the 77mm thin Nikon CP (though I shoot Canon) and it is just amazing with no vignetting, even on a 16mm lens.
|IMG_8168ABCD by citori525|
|McKinley meadow by TimR32225|
from Natural meadows
|Flare-well to a Classic Flying Machine by cjf2|
from Flying Machines
|_DSC2146 by jerste|
from Helios-44 II
|Leopoldsteinersee by RaCor|
from Landscape - Colour #3