If I shift-click to place a building on the same tile multiple times in rapid succession, I am able to get multiple copies of the building on the tile. They all produce resources. This only works on tiles that aren't connected to the HQ.
I noticed this in a single player campaign and was able to reproduce in a daily challenge. I did not try in a multiplayer match. I am currently #1 for today's daily challenge. You can see what I did in the replay.
