Windows.Web.HttpClient: Cookies will not be sent - cookies

Question

I send a HTTP Get Request with a Basic Authentification to the Login-Endpoint of the Host:
request = new HttpRequestMessage();
// Configuration Item: Login URL Suffix
request.RequestUri = new Uri(string.Format("https://{0}/{1}", Host, loginSuffix));
request.Method = Windows.Web.Http.HttpMethod.Get;
var info = User + ":" + Password;
var token = Convert.ToBase64String(Encoding.UTF8.GetBytes(info));
request.Headers.Authorization = new HttpCredentialsHeaderValue("Basic", token);
_httpClient = CreateHttpClient(ref cookieManager);
response = await _httpClient.SendRequestAsync(request, HttpCompletionOption.ResponseContentRead);
response.EnsureSuccessStatusCode();
responseBodyAsText = await response.Content.ReadAsStringAsync();
The HttpClient is created with a Filter, to set Cookies later:
private HttpClient CreateHttpClient(ref HttpCookieManager _cookieManager)
{
HttpBaseProtocolFilter _filter = new HttpBaseProtocolFilter();
HttpClient _httpClient = new Windows.Web.Http.HttpClient(_filter);
_cookieManager = _filter.CookieManager;
return _httpClient;
}
From the Response the SET-COOKIE Header can be read.
string[] Queries;
response.Headers.TryGetValue("Set-Cookie", out tmpString);
if (tmpString != null)
Queries = tmpString.Split(new string[] { ";" }, StringSplitOptions.RemoveEmptyEntries);
I´m looking for a Cookie with a defined Name (CookieKeyName), which will be set in the next Request.
foreach (var query in Queries)
{
if (query.Contains(CookieKeyName))
{
staticCookieKey = query.Substring(0, query.IndexOf("="));
staticCookieValue = query.Substring(query.IndexOf("=") + 1);
}
}
I would expect, that the HttpClient will use the received Set-Cookie in the response for this URL as Cookie in every following Request automatically.
I´m preparing the next Request and setting the Cookie by myself:
request.RequestUri = new Uri(string.Format("https://{0}/qcbin", Host));
request.Method = Windows.Web.Http.HttpMethod.Get;
HttpCookie _cookie = new Windows.Web.Http.HttpCookie(staticCookieKey, Host, "/");
_cookie.Value = staticCookieValue;
bool replaced = cookieManager.SetCookie(_cookie);
The following Sending of the Requests provides to a Web Exception 401, because the Server expects for this URL the previously in the Response received Cookie.
response = await _httpClient.SendRequestAsync(request, HttpCompletionOption.ResponseContentRead);
response.EnsureSuccessStatusCode();
responseBodyAsText = await response.Content.ReadAsStringAsync();
Looking with Fiddler on the Line, the second Request contains no Cookie Header. Even Setting of the Cookie in CookieManager nor the proceeding of the Set-Cookie i the first Response by the HttpClient is working.
Hint: The length of the value of the Cookies is about 6000 chars (coming from a IBM Data Power).
Thank you in advance for help.