Problem with zug grain

[rabiesinfrance]

It appears that a 'top coat' is coming off, leaving black marks. Top quality zugs. Is this usual? For reference, the black marks have appeared at a) pressure points i.e. where laces press into the tongue, b) flex points in the upper, c) points of high contact i.e. heel counter.

With the maker at mo for testing.

Bengal - you seems to be one of the most knowledgeable people here. Any thoughts?