How to delete cookies from WKHttpCookieStore?

iOS 11 brings some updates for WKWebView including cookies managment. I've started migrating my app from UIWebView and ran into a problem: even though WKHttpCookieStore provides a method for deleting cookies (deleteCookie:completionHandler:, Xamarin wrapper: DeleteCookieAsync), in fact it doesn't delete all cookies. Here is my code:

WKHttpCookieStore cookieStore = WKWebsiteDataStore.DefaultDataStore.HttpCookieStore;

// Delete all cookies
NSHttpCookie[] allCookies = await cookieStore.GetAllCookiesAsync();
foreach (NSHttpCookie cookieToDelete in allCookies)
{
    await cookieStore.DeleteCookieAsync(cookieToDelete);
}

NSHttpCookie[] newCookies = await cookieStore.GetAllCookiesAsync();
// why newCookies is not an empty array?

myWkWebView.LoadRequest(new NSUrlRequest(new NSUrl("https://facebook.com/")));

For example, this cookie is being deleted:

NSHTTPCookie    
version:1   
name:c_user     
value:100015842...  
expiresDate:'2017-12-27 07:37:39 +0000'     
created:'2017-09-28 07:39:01 +0000'     
sessionOnly:FALSE   
domain:.facebook.com    
partition:none  
path:/  
isSecure:TRUE  
path:"/" 
isSecure:TRUE

But this one isn't:

NSHTTPCookie    
version:1   
name:sb     
value:bKbMW......OJ1V   
expiresDate:'2019-09-28 07:37:39 +0000'     
created:'2017-09-28 07:39:15 +0000'     
sessionOnly:FALSE   
domain:.facebook.com    
partition:none  
path:/  
isSecure:TRUE  
path:"/" 
isSecure:TRUE

Same problem with native Swift app. I'm quite confused since similar code works just fine with NSHttpCookieStorage + UIWebView.

Is this expected behavior? If so, why? Is there a way to clean cookies in WKHttpCookieStore?

Solution

Update: Previously I filled a bugreport at bugreport.apple.com and now I can confirm this is fixed in iOS 12.

I jumped to conclusion that it's an iOS bug. So, instead of deleting cookies now I'm replacing them with cookies with an empty value:

NSDictionary properties = NSDictionary.FromObjectsAndKeys(
    objects: new NSObject[] 
    {
        new NSString(cookieToDelete.Name ?? ""),
        new NSString(""),
        new NSString(cookieToDelete.Path ?? ""),
        new NSString(cookieToDelete.Domain ?? ""),
    },
    keys: new NSObject[]    
    { 
        NSHttpCookie.KeyName,
        NSHttpCookie.KeyValue,
        NSHttpCookie.KeyPath,
        NSHttpCookie.KeyDomain,
    }
);
NSHttpCookie cookieToReplace = NSHttpCookie.CookieFromProperties(properties);
await cookieStore.SetCookieAsync(cookieToReplace);