When claiming mileage for a self-owned business there is a radio button to select whether the mileage was all business related or if some of the mileage was non-business related and some was for personal use. I selected for both business and self-use and every time I went back to the screen with the radio button the other option for business only was selected. This in turn caused a large return for mileage which was not correct. To get around it I entered only the mileage related to my business, but this will cause improper calculations. When checking my return it was trying to deduct like $5k for mileage which is ridiculous and I had to go back and correct it.
The problem is, when you go back, it defaults into the original answer. So every time you go to that section again, you must make sure the questions are answered properly.
If something is inaccurate at this point, you may want to delete schedule C or the vehicle worksheet. Then clear your cache and cookies, then re-enter and then do not go back into that section.