This dupe has managed to get line of sight through the floor in order to build a liquid shutoff.
I have seen this happen if, for example, a tile has recently been completed, but the day is about 1/3 over and no floor tiles have been built, nor do I recall any being built the previous cycle.
From my point of view it looks like he just randomly decided to build something through the floor.
The supply errand had already been done before the cycle started, I believe, and I don't recall if it was this dupe who did it.
Steps to Reproduce
This issue has not been confirmed by a developer yet.