Grandpa and door that kept unlocking

True story.  Way back in the hills of West Virginia, up a holler, there was an old house.  An old homestead, that my Great, great Grandparents lived in.  My grandfather used to spend a lot of time there, after all it was his grandparents house.  Who doesn't love staying with their grandparents?
Now back in the day, there was a lot of ghost stories shared, and people would hear and see things that were not there.  Not much different then today.  I remember setting on my grandparents back porch, at night, with only the warm light from the kitchen, shining dimly, though the window.  I would listen to the croaking of the tree frogs, and crickets in between the stories, that my grandparents shared.  My grandpa would be stretched out on the swing and my grandma was sitting in a wooden rocker beside my mom.  Dad would usually set on the edge of the porch.  This was where we shared so much.  Sad to say I don't do this much anymore.  I do miss it.  It was a special time.
Well, back to my story.  Not a long story.  This is mainly written down, so that my girls, will be able to be part of the stories of the past.  Their past!
My Grandpa said this had happened many times.  Not just once. 
There was a wooden door, for his bedroom, that would lock with a skeleton key.  You know those pretty keys that you always see in horror movies?  Well, that is the one.  He said he would go to bed at night and lock the door.  Grandpa would go over, and lie down.  He would be there a short time and the door would unlock.  He said, he would here....Click.  Then the door would unlock.  He would go back over and lock it again.  Click and it opened again.  Now I feel the need to tell you, no one was on the other side unlocking it.  All were in bed.  So this wasn't a scared child being toyed with.  Grandpa said he would even jiggle the knob to make sure it was locked.  It would be.  He would go back to bed and it would unlock again. 
This happened, time and time again.  Not just once.  Now tell me what do you think this was all about?  I wish I could have stayed there.  Just once, and been able to experience what my papaw did.