C# Compare strings with umlaut strange results

I use string.Compare(strA, strB, true, CultureInfo.CurrentCulture); and dont unterstand the result. CurrentCulture is "de-DE".

string.Compare( "o", "ö", true, CultureInfo.CurrentCulture) // result: -1 
string.Compare( "d", "f", true, CultureInfo.CurrentCulture) // result: -1 
string.Compare( "dx", "fa", true, CultureInfo.CurrentCulture) // result: -1 
string.Compare( "ox", "öa", true, CultureInfo.CurrentCulture) // result: 1 
string.Compare( "oa", "öx", true, CultureInfo.CurrentCulture) // result: -1

Why the result depends on the second letter to get different results at last 2 lines? If o ist first and ö is next should line 4 not also return -1? Can someone explain this?

To explain why i have problems with this Compare some code:

class Program
    {
        public class ComparerB : IComparer<string>
        {
            public int Compare(string x, string y)
            {
                return string.CompareOrdinal(x, y);
            }
        }

        public class ComparerA : IComparer<string>
        {
            public int Compare(string x, string y)
            {
                return string.Compare(x, y, true, CultureInfo.CurrentCulture);
            }
        }

        static void Main(string[] args)
        {
            List<string> list = new List<string>();
            list.Add("Update");
            list.Add("Ö3 Greatest Hits");
            list.Add("Dont sleep");
            list.Add("Friends");
            list.Add("Dart vadder");
            list.Add("Family");
            list.Add("Oxfort");
            list.Add("Ödipus");
            list.Add("Oasis");
            list.Add("Österreich");
            list.Add("Panda");

            list.Sort(new ComparerA());
            foreach (var item in list)
            {
                Console.WriteLine(item);
            }
            Console.WriteLine();
            list.Sort(new ComparerB());
            foreach (var item in list)
            {
                Console.WriteLine(item);
            }

            Console.ReadLine();
        }
    }

Using ComparerA the result is(mixed Ö and O):

Dart vadder
Dont sleep
Family
Friends
Ö3 Greatest Hits
Oasis
Ödipus
Österreich
Oxfort
Panda
Update

Using ComparerB the result is(Ö at end of list):

Dart vadder
Dont sleep
Family
Friends
Oasis
Oxfort
Panda
Update
Ö3 Greatest Hits
Ödipus
Österreich

But what i need is this(Ö after O):

Dart vadder
Dont sleep
Family
Friends
Oasis
Oxfort
Ö3 Greatest Hits
Ödipus
Österreich
Panda
Update