I think maybe you do have some residents there. It's an old custom in many cultures that when there is a death, especially of it occurs in the house, that you cover all the mirrors immediately and open a window. Being of Celtic origin, I am not ashamed to say that my family has followed this tradition for generations. You cover the mirror so that the spirit cannot take up residence in it, and stay in the house. You open the window to give the spirit a place to escape to. Perhaps, your mirror was commandeered for a bit.
My paternal grandmother could see souls. She was from the days when you still laid your loved ones out on the dining room table and had the viewing at home. She would sit vigil at the viewing until she was sure the soul had left. No one in the family thought this was crazy. It was a kind of accepted thing for us.
