Database oversight. In 1.7 and before, African cultures were extremely general, and the only culture from modern day Senegal east to Lake Chad was "Mali". So all those countries, Mali, Songhai, the Hausa, and Kanem-Bornu had "Mali" culture. In 1.8 they added a lot of new African cultures and culture groups. It looks like they forget to change the culture in the country file. That's a bug -they fixed it in the Borno province.