I'm having the same issue, I followed the steps above about exporting to the default folder, which it worked, so now I can select my custom leaf... BUT it doesn't show up when I use it, It shows up when I Edit 3D component, I attached the two pics of what I see, when I edit the door it self, it allows me to change the color only, I'm unable to see the Iron work in the glass that I made. which is the important part, then the other picture I attached is what it looks like in the model. 3rd attached pic is showing in settings that the custom leave "stained glass" is selected, but just doesn't seem to work.