Edit: Apologies for the "do" in the title. I initially wrote something like "Buttons do not scale properly", but upon closer examination it seems like they do, but it's rather a design limitation. Whether intentional or not, I am not certain.

I was making an add-on for a resource pack to enable it to use JEI, and came across this.

Notice the buttons on the page selection, and recipe type selection. These do not scale properly. For reference, this is button_enabled in the resource pack I am making:

As everything aligns itself with the lower left hand corner of the sprite, repeating the central 14x14 pixels of the sprite as needed, until 2 pixels away from the edge of the button. Then, it simply uses the outer 2 pixels for edging. This ends up breaking any sort of edging that the texture may use.

This works fine - technically - with the default textures for buttons, it does make texturing very annoying. A 2px edge is not a lot to work with. Any kind of detailing with that res is either incredibly simplistic or nigh impossible to do.

As the smallest button size in the UI - to my knowledge - is 13x13, this 2 px edge restriction seems unnecessary. It would be nice to see this be raised to a 4 or larger edge. Again, unless I am wrong - the smallest button is 13x13, so you could logically use the outer 6 px just fine.

Thanks for the suggestion! I didn't design this with that type of texture in mind, but the system I have makes it easy to support with a small change.
I have added support for 6px on the buttons and the search bar.