Building (Just Import?) being REALLY weird.
This is a genuinely puzzling issue. When importing a building, blocks randomly aren't what they should be - see here for a video download. The blocks in the floor, according to the PNG, are all "stone". That's been checked. But when importing (and possibly when building - who knows?!) it's not right - some of it is changed to dirt. And the weird thing is, reimporting will fix it, and importing again will break it again.