Question about my friend's behavior - he likes hiding from people

I am concerned about a friend of mine who has an obsession with hiding from people, stalking his family members, moving around places stealthily and the like. He lives on a farm and regularly tries to traverse the estate without being seen by the employees. He likes using the back doors of buildings and just generally being a ghost of sorts. He is talkative as hell at the lunch table, he's got plenty of social skills and such. He's a completely normal person aside from that he tries to walk home in the most remote locations or by hiding behind bushes to keep from being seen. If anyone knows anything about what might be causing this, or have had a experience with a friend or loved one displaying similar behaviors.