Good afternoon!
My question is about the margin in the display of an image in any conditions. I have two images, here they are. These are the backgrounds for the interface buttons.
The difference between them is that the image that is filled with color, neither through Border nor through Box, does not want to maintain its shape properly when scaled horizontally. The second image, which is hollow, maintains its shape perfectly in the Box mode.

They are almost identical in shape.
What’s the deal here? What’s the critical difference between them for the engine? What does it depend on?
Please help me understand so that I can draw these d*mned buttons backgrounds correctly in the future.
