Blender 2.78. i have a model that as best i can tell has all of these for every object on every layer:
- all normals correct
- no doubles
- no internal faces
- no loose geometry
- fully manifold
the three cutouts for objects are to be applied using boolean ops to carve away affected geometry; lift guide, glue plugs, and lift nuts. the first two apply properly. when the boolean op for lift nuts is added, the window clip disappears.
i've browsed page after page of boolean op problems here and elsewhere and gone over my model intently. i don't think i've missed something so then i'm left considering that i'm naive to some aspect of this.