I happened to be sitting in my office when I read the comments on the miniature, and just had to laugh. On my desk is a picture of my son, exactly like the one on my bedside table. Maybe LJ is just so devoted to Willie that he brought two miniatures, one for his office and one for his private quarters... and since he's new in town and probably not even settled, he just happened to still have both when Jamie walked in the door.
Really, I do agree that it's probably just a plot convenience. This is the beauty (for me) of a re-kilt. It certainly never crossed my mind the first time through to stop and notice all these details -- I was trying to race through it all as quickly as possible to find out what happened!