Hue-Saturation without effect

[Krikor]

Hi,
I have an image formed by a gradient between red and white.
Basically the red saturation is 100% on the left and decreases as it goes to the right.

My question is about the Colors - Hue-Saturation... filter

If I make a selection on this image and apply a saturation adjustment via Colors - Saturation..., the change is visible, whether I increase or decrease the saturation.


However, if the adjustment is done via Colors - Hue Saturation... the change is only visible if I reduce the saturation. If the saturation is increased, even to 100%, nothing is noticeable.


Is it a bug or is this filter behaving as it should?

Thx!