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?