OK, I've taken a look into many of my mission Dyn files with wordpad. It seems only Unit Family 2 bombers with a Catagory 3 or 10 (dive bombers) and Catagory 5 (tactical bombers) were switched to Unit Family 1 after editing with MB. Bombers with Unit Family 2, Catagory 2 (level bombers) remain as Unit Family 2 after editing with MB. Any guesses as to why MB changes them to Unit Family 1 after editing? Is it possible that MB considers anything other than level bombers to be fighter bombers and tries to correct what it thinks is a DP mistake?
Only Microsoft knows but maybe play them both ways by leaving their corrections as is and make another one read only so only you can edit it. It might crash if it can’t edit it who knows but if you don’t try new things and study nothing is gonna make any sense.