NSURLSessionResponseBecomeDownload and NSURLSessionDownloadTask delegate issue

Question

In my project, I start a NSURLSessionDataTask to check the header of a request, and if they're right, I turn the request into a download or I just discard it:

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
        if (XYZ) {
            completionHandler(NSURLSessionResponseCancel);
        }
        else {
            completionHandler(NSURLSessionResponseBecomeDownload);
        }
    }
}

However, I am incurring into a problem: once the session is turned into NSURLSessionDownloadTask, sometimes nothing happens and - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location isn't called at all, and - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error either.

What's happening here? Does it make sense?!

––– EDIT –––

Apparently this solves the problem?

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask
{
    // Resume the Download Task manually because apparently iOS does not do it automatically?!
    [downloadTask resume];
}