The Bug
I was Testing with the Border today and using Debug Chunk borders.
I went to the worldborder and noticed that the Chunk borders render on top of the worldborder instead of behind it.
How to Reproduce
1. Set the worldborder to 60
2. Go to the border
3. Turn on Chunk borders
4. You will see the red line rendering on top of the border with all the other lines of the Chunk border
I can't reproduce, the color is subtly different when the world border overlaps