I'm moving this to the object creation forum. You're more likely to find help there. Also I remember someone in that forum was having the same problem with a door. You may want to look for that and see if they got a solution.
I've tried too to clone a window, and I guess that Delphy's export plugin and/or the Mesh Tool don't manage correctly the "hole material" that is embedded in the "wallshadow" mesh (that "creates a hole" with the same shape of the window/door).
If I'm right, no editing will be possible for windows/doors/arches until the MeshTool isn't updated.
Anyway, I hope to be wrong
I've finally started my Journal. Information only, no questions.