My son (17yo) does this 3-4 times a year - he will be rushing out somewhere, will pull the door closed behind him, but not check to see if it clicked shut. He did it this morning when he went out for the day, which freaked me out because I would normally have been in the office on a Tuesday. The house would have been empty until at least 5pm, with an open door.
Obviously I'll be speaking to him (again) but I'm wondering if it's a common problem.