I just spent 10 minutes swearing profusely.
I forgot to turn off symmetry. So I'm making a minor detail. Not much really, just a platform for rotating eye candy. But I was a bit undecided on how I wanted it to look. Naturally, I'm adding and removing blocks, testing things out and adjusting. Then I notice I've got blocks floating off in space. Sigh, turn off symmetry, delete the junk, moving on.
20 minutes later I realize I missed some. My platform is mirrored right in the middle of my elevator logic.
I think I could have made a sailor blush.