Color level adjustment of Layer mask can lead to color distortion - bug ?

[Grobe]

I don't have the full story of the image. I can see if I can find the source image (or similar) and see if I can make to reproduce the results. If I get this, I can try to describe how to reproduce.

Btw: somehow I'm not receiving any emails notifying of post at this forum, I check once a day normally.