The use of O_BINARY where available was in the very first back-of-the-envelope suggestion from Tom Christiansen in March 2000. I admit to not really thinking through the consequences but clearly Tom imagined that most temp files would be binary rather than text. There is a bit of a backwards compatibility issue with changing the default to text, so any option would have to be provided in addition to current usage. I would be open to a TEXTMODE patch that has been tested on windows. I've never really had a Windows box for testing things on and no user has ever offered patches to get it working properly on windows.