Reports ” -2Thumbnails will be generated”

I use this to disable *all* thumbnails. The “Disable Thumbnails” screen says:

You currently have 8 thumbnails registered. It means, if you upload an image, it’ll generate 8 duplicates along with the original image.

Drag the image sizes you don’t want to generate to the right side. The image sizes on the left will be generated.

10 Thumbnails disabled

-2 Thumbnails will be generated

Any idea how to fix this? To be clear, the plugin is working – there are no thumbnails being generated.