It seems like every time I start a new game some of my old unit designs carry forward and end up cluttering my train units window. This could be a nice idea if it stayed with the sole faction and only units I've designed.

However! Even the basic peasant, peon, pioneer, etc get duplicates that change only the portrait, clothes etc. No stats, costs or anything else differ. The only unit that seems to be immune from this duplication would be the Caravan for whatever reason.