panel.png (legacy/textures/gui/sprites/tiles/panel.png) is weird. Let's go over it and why I'd like for it to be changed for consistency for those who want to port over the console texture packs specifically.

As you know, panel.png is responsible for the background of every console screen currently in the mod. It's a 96x96 image that makes up the whole background of the screen.

However, despite being able to be evenly cut into 32x32 pieces (like it is over on console), the tiling for this suggests otherwise when you use another pack's more intricate/detailed panel tiles, such as Steampunk: _{(ignore the fact it's not all of steampunk's ui here. i wasn't done doing that but wanted to get this issue posted)}

Ideally, screens should proper stretch the area inbetween the corners for the sides-- not whatever's going on here that I can only really show through packs like Steampunk.
Here's a visual example of how clean panel.png can be cut using solid colors.

The four corners should remain untouched, while orange, green, blue, and pink get stretched (or tiled, not sure how console handles it. Can someone rectify this?) between the corners, like so in this quick mockup:

I'm fully aware this would likely mean you'd have to redo all the screens to follow this, but for the sake of headaches for us trying to port and use console's packs for ourselves, it'd help a lot.

Fixed in version 1.4, this a simple config issue, these "custom size" (nine slice, better said) textures are easily configured by the .mcmeta sprite file, the "border" value should be the the width/height of the piece/tile from the texture.