if u only had youmu on the photo it might make sense that it didnt work but if u had a photo with both youmu and the ghost in it and it still didnt work then i guess it was really a bug. bugs that only happen for some people are the most annoying type of bugs.
as a dev for business software i hate it when the customer gets a bug that i cant reproduce on my system. how the heck is a dev supposed to find/fix those bugs that decide to appear randomly? xD