Hello,

While attempting to create something (from a Siril-generated .fits file)
that Darktable interprets as a colour image, I noticed some mildly
infuriating behaviour in the Curves and Levels tool (which might mean that
it affects other channel-handling tools too):

  - when I edit the Value channel, the result is as if I'm editing the Green
    channel.
  - when I edit the Green channel, nothing happens.
  - red and blue channels behave as expected.

Naturally, auto levels very much does the wrong thing.

I've attached a (severely cropped) example image.