This happens to me constantly and I've basically stopped being surprised by it. The most baffling one was my car keys turning up in the airing cupboard upstairs after I'd torn the kitchen apart looking for them for 20 minutes. Nobody else in the house, no logical explanation.
What I find interesting is that it tends to cluster. You'll get nothing for months and then suddenly three or four objects go walkabout in the same week. I've started logging it alongside my EVP sessions and theres a loose correlation with periods of higher activity generally.
Some people say its just absent-mindedness but honestly after 15 years of this stuff you know the difference. Has anyone tried setting up a camera to actually catch an object mid-move? I've been meaning to do this properly but never quite got round to it. Would love to know if anyone's managed to capture anything useful.