The issue is cutting an opening in an existing floor so that in only shows in a new phase.I have created a floor based generic family with an opening tool and added an edge liner as a sweep. It hosts onto the floor and cuts it OK (in section and 3D). BUT in plan view objects below dont show through - see blue dashed on the screen clip. You will see that the red dotted opening>vertical cut show the stair below OK. Have a go (floor opening lined.rfa) and tell me why the opening is opaque!
Playing with the phase, if I change the existing floor to new the stair below shows correctly. Then switch back to its correct phase the stair is hidden again. Do the same with a roof (existing roof, add a hosted lement with a hole as new phase, the apperture is transparant.
The hosted object is cutting the host correctly in 3D and section but not in plan.