[0.299][1Z1][Bug/Gameplay] Pioneer can built on resources multiple times.
If you send a Pioneer to resource you have already built on you can build another building there and get more resoures. You can only seem to select the building on top and it may only show your getting +0.5 Metal from the mine but your total metal income maybe something like +2.0 from being 4 mines there. The color of the building on the map gets darker with each additional building you put down also.
[Suggestion]
While on the topic though I figured I'd mention the balance issue. I don't think it's good to have the pioneers only gather 1/2 the resources especially when it seems like the building cost is the same as if a city built it. It really devalues the point of having those buildings. Plus some things like shards you actually need to use the Pioneer bug to get full credit for(aka +1). I think the bonuses from things like granary, forge, and other future buildings are reason enough to want resources in the cities without unduly penalizing the pioneer setups which are a bit costly when you consider you need both the pioneer unit's cost and the building cost just to setup one. In most games I don't even bother with pioneers until I have lots of extra resources cause the cost vs return is so low.