Mathematica 12.0 returning a imaginary value for a real-valued improper integral

When I use MMA to solve this integral

Integrate[(1 - Cos[x])/( 2 - Cos[x] - Cos[y]), {x, -Pi, Pi}, {y, -Pi, Pi}] 

it returns 8I*Pi*Log[2], which is obviously wrong. If I iteratedly calculate it

Integrate[Integrate[(1 - Cos[x])/(2 - Cos[x] - Cos[y]), {y, -Pi, Pi}], {x, -Pi, Pi}] 

MMA gives 2Pi^2, which is correct. Can anybody give an explaination?