No, The problem is that when form has been maximized there is a distance in the right side of form. In fact, the form has not been completely maximized.
This issue exists in the ASkinEditor only? Or in all apps with active ExtendedBorder?
In all apps with active ExtendedBorder (Windows 10 and 4K monitor) but This problem only sometimes occurs and not always. Whenever I face this problem, I restart the Windows and the problem gets solved.
See screenshot, It is your skin demo v14.10 . Notice the right edge of the form.