Yes, as I said, I checked it out, and I know how it works now. I traced all this back to where user @LVS said something about selecting one or more masks. For the purposes of the changes I’ve proposed, you only ever select one “mask” (where “mask” = parent mask). There’s no point cluttering up a drop-down with sub-masks, since the drop-down would be for selecting which mask one wants to apply settings to, and sub-masks don’t have their own settings.
The current UI, as I mentioned, doesn’t make this obvious. My proposal would.