The disappearing and reappearing thing has happened to me too many times to document. A good friend just refers to the phenomenon as the "house sprites" - not necessarily ghosts, spirits of the recently departed or anything like that but some kind of invisible inhabitant of the house who can occasionally play tricks. Her recommendation is simply to stop still, say out "Put it back" out loud and vehemently, leave the room and then come back in again. She says the object will generally be there, in plain sight.
When a group of us moved into a house in London (the group including Bonnie Shaljean, amongst others) we had a number of moving and disappearing objects. These were seemingly random in what they were and where they would reappear. We did all watch one night as a heavy wooden chair fell over, with no apparent reason and no earth tremors. The best disappearance by far was when all the dinner plates in the house disappeared one evening when we were entertaining the Watersons to dinner. We looked high and low and eventually served the meal on whatever we could use - flan dishes etc - and two days later all the plates reappeared on the draining board by the sink in the kitchen. We tried to blame this on one hapless house resident who was more than usually disorganised in his habits, but we couldn't find a viable way he'd done it. Oh well.