从字符声明字符串会产生意外结果。为什么会这样呢？

半天寻找这个错误。为什么在第三种情况下出现意外结果？

        // case 1
        string value1 = "a" + "a" + "A";  
        byte[] asciiBytes1 = Encoding.ASCII.GetBytes(value1); // expected: 97 - 97 - 65
        Console.WriteLine(string.Join(" - ", asciiBytes1));   //   result: 97 - 97 - 65

        // case 2
        string value21 = 'a' + "A"; 
        byte[] asciiBytes21 = Encoding.ASCII.GetBytes(value21); // expected: 97 - 65
        Console.WriteLine(string.Join(" - ", asciiBytes21));    //   result: 97 - 65 

        // case 3
        string value22 = 'a' + 'a' + "A"; 
        byte[] asciiBytes22 = Encoding.ASCII.GetBytes(value22); // expected: 97 - 97 - 65
        Console.WriteLine(string.Join(" - ", asciiBytes22));    //   result: 49 - 57 - 52 - 65