As your other posts have indicated, the image is not a "flag that the Balkan muslims flew during World War II." It is the insignia of the 13th Waffen-SS Division. There is clearly a difference between 21,000 Nazi soldiers and a region's entire population.
...which was recruited by al-Husseini and Himmler as an all-muslim Balkan Nazi division. It's clear what side the muslims took in WWII. To them it was just another opportunity to shoot Serbs and participate in the extermination of the Jews.