I used lower land on a hill within my city (it looked ugly). As a result the buildings, that were built on this hill, were flying in the air afterwards. This also happened to a neigbouring lost library. The city buildings were put back on the ground when the city grew, so about 40 turns later. The lost library remained in the air.

Therefore lower land should trigger some routine to place assets back on the ground. I unfortunately did not think about raise land at the time.