See my screenshot:
What I’ve got going on in the image is a Procedural Foliage Spawner spawning some foliage with a Procedural Foliage Blocking Volume preventing the growth of foliage in that cylindrical space. I then went into Foliage Mode and I have the FOLIAGE filter set to TRUE. My assumption here is that (per the tool tip) I would be allowed to paint foliage on top of this blocking volume!!! That does NOT seem to be the case.
My question, then, is how is the “Foliage” filter within Foliage Mode supposed to behave? I’m clearly off in my assumptions.