False positive with ALAssetsLibrary

[swt2c]

When using ALAssetsLibrary, I'm seeing an "Invalid concurrent access to managed object calling 'release":

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    // code
}];

It seems this may be a false positive? It looks like the Apple code may be creating the ALAssetsGroup on another thread, and this warning comes when it is released on the main thread.