NSURLCache doesn't cache

I'm using Xcode 6.1 (6A1030), both iOS7 & iOS8 Simulators.

NSURLCache does not seem to cache anything. I use the "Cache-Control" header. My server returns the Cache-Control header with 'max-age=6000'.

In this example, I tamper a request from Google, which is also not cached:

AppDelegate:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    var URLCache = NSURLCache(memoryCapacity: 500 * 1024 * 1024, diskCapacity: 500 * 1024 * 1024, diskPath: "bla")
    NSURLCache.setSharedURLCache(URLCache)
    sleep(1)
    return true
}

Then I start the connection:

    let urlPath: String = "http://www.google.com"
    var url: NSURL = NSURL(string: urlPath)!

    var request: NSURLRequest = NSURLRequest(URL: url, cachePolicy: NSURLRequestCachePolicy.ReturnCacheDataElseLoad, timeoutInterval: 5000)
    var cachedURLResponse = NSURLCache.sharedURLCache().cachedResponseForRequest(request)

    // cachedURLResponse is always nil

    var connection: NSURLConnection = NSURLConnection(request: request, delegate: self, startImmediately: true)!
    connection.start()

And before the caching of the response, I add the Cache-Control header:

func connection(connection: NSURLConnection, willCacheResponse cachedResponse: NSCachedURLResponse) -> NSCachedURLResponse? {
    var HTTPResponse = cachedResponse.response as NSHTTPURLResponse
    var modifiedHeaders = NSMutableDictionary(dictionary: HTTPResponse.allHeaderFields)
    modifiedHeaders["Cache-Control"] = "max-age=6000"
    modifiedHeaders.removeObjectForKey("Expires")
    var modifiedResponse = NSHTTPURLResponse(URL: HTTPResponse.URL!, statusCode: HTTPResponse.statusCode, HTTPVersion: "HTTP/1.1", headerFields: modifiedHeaders)
    return NSCachedURLResponse(response: modifiedResponse!, data: cachedResponse.data, userInfo: cachedResponse.userInfo, storagePolicy: cachedResponse.storagePolicy)
}

The modified response looks like this:

{ URL: http://www.google.com/?gfe_rd=cr&ei=MSBGVKe7AeeI8QepoYGgCg } { status code: 200, headers { "Alternate-Protocol" = "80:quic,p=0.01"; "Cache-Control" = "max-age=6000"; "Content-Type" = "text/html; charset=windows-1255"; Date = "Tue, 21 Oct 2014 08:58:25 GMT"; Server = gws; "Transfer-Encoding" = Identity; "X-Frame-Options" = SAMEORIGIN; "X-XSS-Protection" = "1; mode=block"; } }

And yet, 'cachedResponseForRequest' returns nil every time, and a new server request is sent every time.

Am I doing something wrong? Thanks a lot for your help!