Hi, Michael,

i've uploaded a similar file to http://www.earthcontrol.de/tempfiles/boole_bug1.3dm
the artefact is appearing only on one side here.

hope it helps

btw, again, i have to say what a fun it is to create things with MoI..

how about adding the ability to switch certain objects to outline or wireframe mode ? this could ease up things when for example building rooms inside a building.