When I use Design Center to drag and drop a layout in a drawing, the scale factors of the blocks are wrong in the target drawing. Typically, even though the block properties show Block Unit=Millimeters; Unit factor=1; and Scale X,Y,Z are all = 1, they are scaled to imperial and I'm forced to scale them back manually by 0.03937. At the same time, the size of the paper is correct (A0 metric). INSUNITS are the same (Millimeters) in both source and target files. The source blocks are in mm scale 1=1 as well.
I've seen a few similar old posts in the forums but they haven't been answered so far.