darktable contrast equalizer creates ghost lines

While working on DSC_0169.NEF from Landing doves - help needed by @sotsoguk, I used contrast equalizer and noticed some ghost lines appear next to the chimney:

DSC_0169_07.NEF.xmp (35.5 KB)
I turned that instance of the module off and used a new one with different settings, which worked fine. I am wondering if this is a bug or is just peculiar to the settings I used?

Yes, these artifacts are the results of the module. Just decrease the line in the “coarse” region.