I removed the pieces all the way down to the foundations and still didn’t have any luck. Then I moved a thrall, a Stygian bed and a t3 planter that were all near, but didn’t seem that close, and suddenly I could place pieces again.
The area is still weird though, as I’m unable to place items on some of the foundations now. Oh well, at least the building is finished.
Another frustrating one that I’ve seen is the inability to snap in a ceiling tile at the base of steps when building downward from above. I wonder if glitches like this have shown up as a result of the devs trying to squash exploits or some such.
I’m just happy the stair corners work properly though. I believe @Multigun was instrumental in tracking down the blueprint/socket issues on those, wonder if they could see any similar anomalies with the roof corner/door frame or stair-base/ceiling socket interactions…