It's late Industrial Age, and I've got my workers busily foresting the tundra tiles they mined years ago when I automated them after getting the railroad up. Anyway, I move one onto a tile where I see a mine and it tells me I'm on forest. Check the top left corner of the screen shot below. So I chop the forest, to see what will happen, and sure enough the mine is still showing. I figured it was just a graphic bug, so I right click on the tile and it's actually producing two shields! Woohoo, free mine!

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