I have only seen this happen a couple of times. When using a locally attached printer (via usb) I have noticed at a couple of my clients' locations that this seems to break the driver. At one (using a Magicolor 2530) I went to share it off to other computers (all using Windows 7). The next day the client called me and said that the printer was acting weird and printing off their pamphlets with bad quality. I went to investigate the issue and saw what they were talking about. It looked as though it was printing off in four-color mode or something. I uninstalled and reinstalled the driver. This fixed it again for about a day. I soon realized that everytime I shared it off this happened. I turned off printer sharing and the problem has not returned.