Hopefully you'll get this, I see your post is several weeks old. Sounds to me like an obsessive compulsive thing. Bet it started as a simple thing and eventually turned into a habit. Does he have other obsessive tendencies?? If not, then maybe you can figure out a way to remind him without nagging when he does it (easier said than done!). Unless of course he has other tendencies in which case, you may want to see a therapist so he can learn to adjust to OCD.