I've noticed a mapping bug during the repaint of a GP-38, which only affects the cabin doors. If you paint on one door the same effect appears automatically on the other door. Maybe it is caused by an texture overlay in the UV map.
Just discovered this today. Did u ever submit a ticket to tech support? Ur work is excellent, btw. Rare to have front and back cabin doors having different colors or designs irl, but when it does, this mapping flaw ruins the design. There may be a similar issue on the SD40 with the left front/back right handrails being the same...I'll have to go back and check.