Z3 Roadster (E36/7) seat surface problem

When I bought my 2001 Z3 in early July 2012, all the seat surfaces were clean and in good shape. I noticed, however, that the center panel in the driver's seat (the horizontal surface, not the back) was unusually hard and stiff. The other panels are supple and soft, no rips, no tears. I had thought the seats were leather covered, but this may be a plastic surface. Over the past months the stiff panel has cracked and torn. The tears are not in the area where I carry my keys, so they're not to blame. Has anyone else experienced this kind of damage?

I cover the damaged area with a fitted sheepskin insert, but I find this very curious.