Cannot personalise ringtones

On the contacts' pages there is a menu and one option to "Set ringtone". It allows me to select a rintone from the list and plays the tune, but when that contact calls me, the default ringtone is played. On rechecking the contacts ringtone, the selection dot is against the default one again.

Am I missing something? If I am, I cannot find it. Please help me with this one.