GUI gaps when using Inset borders

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  1. What do you want to achieve?
    There are two frames (pictured below), white (behind the red one) and red, they are absolutely the same besides their color (white frame has an outline border to make the issue more explicit).
    When I tried to add an inset border to the red frame, there appeared a white gap on top and the left side, basically the border seems to be unequal on the sides of the frame.
    For some reason this happens when the border thickness is less than 10 pixels. It was 5 pixels on the screenshot, and when I set it to 10 pixels, the white gaps are gone.


  1. What is the issue?
    *Red frame Inset border thickness is 5 pixels.

*Red frame Inset border thickness is 10 pixels.

P.S.
The same happens for surface GUI’s.

  1. What solutions have you tried so far?
    I didn’t find anything related to this yet. It seems to be a glitch.