Why can't I change the ringtone on a Contact?

[AC Question]

I have a Samsung S5 running Lollipop. I have added some custom ringtones to my ringtones folder and can see them when I try to change the default ringtone for the phone but when I go to try and change the ringtone for a contact (so I can have different ringtones for specific contacts), I see the Ringtone setting on the contact and it says it is Default but it won't let me change it.