Substance Painter - Export and then Reimport to Black Mask area


Due to my need to go back and forth from home to lab I exported my “black masks” as white/black textures to Photoshop.

When I went to reattach these masks (importing from separate PSDs) I then reimported them to the black mask area by right clicking and Add bitmap mask. Rather than put these masks back into that black mask area this operation creates a Fill underneath the black mask which I cannot edit.

If I continue to work with these files I edit the “black mask” further white/black masking, and am stuck with an uneditable Fill mask below. I can’t add to or erase this Fill area. This means I can’t ever erase something in that Fill slot.

Since I exported the black mask area I should be able to reimport the same mask image to the black mask area via some operation and not have this messy alternate result. How do I do this?

I see there is a Paste into Mask option when right clicking the black mask, but it is greyed out and I haven’t been able to figure out how to “grab” something to paste into that area, click and drag don’t work either.

Creating bitmap mask on the material color itself creates this problematic Fill.
Creating black mask and THEN making a bitmap mask on the black mask does the same thing.
Is there some sort of “merge Fill to black mask” to make editable option?

It seems like this all should be a very simple click and drag operation.