It happens to me too, right now the only flash meter I have is missing. I had a couple of semi rare tool's bought from the estate of a old friend who had passed away went missing and were gone for eight years. Last fall they just showed up on a shelf one day. Never have figured out how that happened.
What bugs me most of all is a book titled MYSTERIES OF THE UNEXPLAINED that just appeared out of nowhere on my bookshelf. I did not bring it home, and no one else in the house knows anything about it. Its a strange thing to have that happen.