I'm curious, how do you know CONC is build-able? is it the blank building sidebar icon? Slightly related if you look the bib, as well as being simple two parallel lines of dirt, stays after the building is destroyed.
Also, just a thought, but could it be possible that the GDI and Nod logos on the construction yards are drawn on top of the sprite rather than on the actual sprite if you get what i am meaning. I realize however this is unlikely and problematic when it comes to the construction animation but would get around the current problems linked to the whole one MCV, one construction yard game codding.