So far I get this consistently. Others are saying this is not happening to them.
Using level foundations I cannot place thralls onto the map unless I destroy the foundation to expose the ground beneath. I cannot place a bed either on a foundation. I can place them on a ceiling however. The two building foundation this has happened with are the sandstone with the wood top and the new Turanian foundations.
Once you place the thrall on ground you can then put them on the foundations. You get the error but they will stick. However the bed will not because of the overlapping error. This is empty foundation. So there is no overlap.