The only things that actually say in place 100% of the time are Nuka Colas (Regular, Cherry and Quantum).
Sanctuary is especially "haunted" when it comes to decorating. Many, many hours ago, I decorated a metal shack, which I've since taken down. Yesterday, I went to talk to a settler and suddenly, a tea cup, a metal bucket and something else fall out of the blue sky, almost hitting my character on the head! LOL It's a spot across the road, just from where the workbench is. I usually always find stuff there that went missing a long time ago. However, that is certainly NOT the spot where I dropped the items the first time. So weird!
But yea, settlers don't take anything (stuff in containers or otherwise). I placed a metal desk, on top of it, I placed a typewriter. I saw it sunk half in a day later and it was totally gone the next day. It wasn't on the floor under the desk. I've build my Spectacle Island fortress on both concrete and wooden platform foundations, so my guess is that the typewriter is under the house. I haven't bothered looking for it yet. LOL
Oh and the other objects that are actually still sitting on my table and metal shelf are the nice clean glasses that I took from the Institute. They have been sitting in the same place for many, many hours now! So, yay Institute for pretty glasses... now work on the flower vases!