Yes indeed i have used extensively extra.less
I have a default/original style.
I have removed everything from extra.less and after trying again, i still have the same problem. after clicking on the menu that has a drop-down menu, the borders become squares. View attachment borders.mov
My bad, my code theoretically keeps the radius when scrolling and the navigation bar is sticky. I didn't notice you were talking about the problem when the tab is open... But it's weird because originally the open tabs keep their radius, you can test here... So I guess there is some code somewhere that causes this.
That doesn't work either.
I have reduce the issue by changing the background color when hovering. The white makes the problem quite visible, with a blue-ish color it is a bit less visible.