The bug

When loading the world border after loading a world and not moving at all, the border is occasionally rendered as a solid color or a gradient of different colors.

I've attached four screenshots demonstrating the issue.

How to reproduce

1. Create a new superflat world with "The Void" preset
2. Run the command /worldborder center ~ ~ (Don't move after running this command!)
3. Run the command /worldborder set 10
   The border is shown as a solid color