I'd like to report a bug that has been plaguing photoshop for some time. This is to display a histogram for the adjustment layer which is in Clipping Mask mode.
When the adjustment layer is in Clipping mask mode, the histogram that displays in the Properities panel should only be for one layer below. For some reason, all new versions of Photoshop display a histogram for all layers below which I think is a bug and not working properly.
When the adjustment layer is in Clipping mask mode, the histogram should be in Selected Layer mode for the layer below, and it is in Entire Image mode.
As a result, it is impossible to precisely set Levels or Curves, because the histogram does not display the data that the user needs.
Hope something can be done about it.
PS. In the Photoshop CS6 and below this was no issue as everything was working fine with this.
Thank you for for reporting this. My team and I are aware of this issue and have it in our To Do/Backlog. I'm sorry this has been troubling for so many years. We really want to fix this, but the amount of time to fix this will require a lot of time. Apologies again.