Huh, that's the first time i see that, i assume you have non-default fonts or sizes of the window.
I'll try to look into that.
Meanwhile, is it Windows 7 you got there? i can't recall having borders like that.
What, in your opinion, fonts are not default? Win 10 is not usable with default font size at all. And yes I do Windows 7 and Windows 10 both work same. But, as far as I see it, this is not border, it is like background square which changed to front and maybe grown in size. Leave it transparent will not harm the interface. Thanks for reaction.