Form Border Style is not properly displayed

Question

This is one problem I can't understand. I'm using windows 10 and by default the form border should be displayed like this:

But for some reason or the other, my windows form app's form border is like this:

... despite the form border property is set to FixedSingle. I also tried the same with form border property Fixed3D but still it is of no use.

It would be great if someone could guide me about how this can be fixed and the reason my form's border is wired. Please download the images to get a clarity of what I'm asking.

NOTE

Fixed here means to get back the default form border.

I also use Bunifu Framework. However I don't know the relevance it has here

The image attached was taken during debugging