I had new barracks using BCUs requiring new stables and vanilla-tree missile buildings. Whether the building is new or not may have some bearing on it as I seem to remember 1 new building I set up would not even accept one BC unit.

Though it is an interesting thing to suggest the unit_info may have something to do with it. Can you confirm that the BC units displace the correct unit info pics (as if the game ignores the BC units) when right-clicking in the manner I have heretofore listed (in the EDB discussion thread)?