I've luckily never had this happen to me during a few decades living in NJ and across a fair number of vehicles, but if you Google plastic ice scraper scratched windshield, it seems disturbingly common across many different makes of cars....a lot of theories why (plastic coatings on glass, etc), but nothing that seems definitive....the theory I give most credence to is that all cars get some amount of potentially abrasive debris stuck on the glass, and that will end up between the glass and any added layer of snow, ice or frost. When you use even a plastic scraper, that debris can then scratch the glass in some instances if it happens to lie directly under the edge of the scraper or gets caught in it as it gets pushed/dragged across the glass. So, the potential is always there, but it won't always happen. Essentially what Murky is saying above.