Door opens and closes itself.

Yesterday, after work, my wife went upstairs to unwind and I took my turn at the computer in the Library. Shadow, my dog, was dozing on her pillow not far from me. My wife came into the computer room at about 9:30pm and said, "When you were upstairs, why did you open my door and not say anything?" Whoa I replied, I've been right here since I started (about 6:30pm). "Somebody opened the bedroom door about this much (indicating 6 or 8 inches) and when I said, "Yes?". they closed it again." The bedroom door opens from the long upstairs hall. The doors in this house are original, heavy Oak or walnut construction. They do not swing freely. When opening the door it stays in place when pressure is released. It takes some force to swing these doors open or closed. The upstairs hall is pretty much enclosed and not subject to drafts unless the attic door is open and even then I doubt any draft resulting would move one of these doors. I have no idea what open the door or closed it. But I do know these doors do not open and close without some pressure being applied. Finding exterior doors that I know darn good and well were locked...open is far more common than watching a door open and close its self. My dog goes bonkers when anyone other than I or my wife enters. She was quite quiet. We keep our exterior doors locked. Including the one off the western side of the kitchen that we most commonly use. It does swing fairly freely and invites flies in when open. We also keep it locked to keep warm or cool air inside. I have no idea what opened and then closed the door to the room my wife was in. Its just one of several mysteries I'd like to solve about this old house.