I built my base underground as the overworld is covered in biters. When I started deconstructing stuff with bots, I noticed ore showed up. Ore is generated when ANYTHING underground is removed by bots, not just the rocks. Inserters, furnaces, power poles. The upgrade planner has the same behavior.
It's not really game-breaking, because it's only a little ore, and it ties up the bots for a long time. Just annoying.