Unexpected output when using Bayer mode

Hello,
Firstly thank you for the wonderful tool.
I noticed this non-ideal output using the Bayer mode. I uploaded this test image, consisting of just white `#FFFFFF` pixels:

Using, for example, the Red preset palette produces this unexpected output:

despite `#FFFFFF` being one of the palette colours, it is incorrectly producing a red-dithered image.
Similarly, uploading a solid black image produces a red pattern despite `#000000` being in the palette.

This does not seem to affect the Error diffusion methods, all of which work as expected.
An example using a cel shaded illustration, you can see suboptimal result vs. one of the error diffusion.