First the code to reproduce the problem:

string[] array = new[] { "test1", "test2" };
byte[] bytes = MessagePackSerializer.Typeless.Serialize(array);
object obj = MessagePackSerializer.Typeless.Deserialize(bytes);

If you debug the code, you see that the result in the obj variable is an object array (object[]) and not a string array. The object array contains the strings, but I need the array itself to be of type string[] or I get an InvalidCastException in other places of my code. There is the same problem if the string array is nested in another object array.