Do you use your fingertips or nails when you depress the buttons?
I've seen this before in a few other cars. The early Cadillac CTS was notorious for this. They always replaced them under warranty. I imagine you'll get BMW to do the same.
DON'T try to use a degreaser or anything else on them. You'll just wipe out the rest of the paint and for sure be denied any sort of warranty coverage.
What's your build date?