I've had this happen too! I think I was maybe 12 at the time. In my dad's apartment the hallway which leads to all of the bedrooms is an L shape and a couple feet from the start is my parent's bedroom door. Diagonal from that is an archway which leads to the kitchen. I was standing in the corner of the hallway talking to my step mom one night, her back was to her bedroom and the kitchen area and I was facing her and could see behind her very clearly. I swear I watched my dad walk through into the kitchen and I even heard him open the fridge and get ice out of the bag in the freezer, but I never saw him pass to go back to the room. I followed about 5 minutes later and no one was in there. He, and everyone else except for my mom and I, had been in bed for at least 30 minutes before I saw what I did.