It is stored in filter layer but when layer parameters are edited again saturation is reset to 0.
Thanks for your report! I am able to reproduce the issue.
Created attachment 104998 [details] Fix for incorrect restoration of saturation slider In the UI file (wdg_hsv_adjustment.ui), the minimum value for saturationSpinBox was not set, and hence was taken as default 0, and the minimum value for saturationSlider was set to 0. I added them and now it seems to work fine.
Thanks for the patch!
Git commit 581b87f6469894f6c7ee1d2f19bbf34883b869be by Boudewijn Rempt. Committed on 25/04/2017 at 12:38. Pushed by rempt into branch 'master'. This fixes loading a hsv adjustment from a filter layer and editing them. M +5 -2 plugins/filters/colorsfilters/wdg_hsv_adjustment.ui https://commits.kde.org/krita/581b87f6469894f6c7ee1d2f19bbf34883b869be
Can still be reproduced.
I've checked current 4.0 alpha and it seems to work fine.
Okay, closing.