Why does my aunt's cat do this?

alright so my aunt has 2 cats, felix and oatmeal. and well for as long as i've known oatmeal (for 6 years) i've notice that even if he or felix uses the literbox just once...when he goes for it again he always does his buisness next to the litter box...my uncle does clean the litter box daily so it's not a cleaning problem....you think oatmeal is just picky? i've always found that weird..