i think it was because i have some extra layers and they caused confusion. I thought that I had replicated everything, so it must be something else in my game that confuses things.
I see! In Construct, layers trump Z-elevation, which can break the perspective. In order for Z-elevation to work with perspective the objects whose Z-elevation you want to manipulate (with my addon or manually or in another way) have to belong to the same layer.
This gave me headaches so many times…!