Odd results?

public static void Main(string[] args)
        {
            var x = Flip(10000);
            var y = FlipNew(10000);
            ////var bench = new ReverseBench();
            ////bench.FlipInSets64Bit();
            //BenchmarkRunner.Run<ReverseBench>();
        }

        public unsafe static ulong Flip(ulong val)
        {
            //ulong val = 0;
            //Unsafe.Write(&val, value);
            val = (val << 56)
                | ((val & 0xFF00U) << 40)
                | ((val & 0xFF0000U) << 24)
                | ((val & 0xFF000000U) << 8)
                | ((val & 0xFF00000000U) >> 8)
                | ((val & 0xFF0000000000U) >> 24)
                | ((val & 0xFF000000000000UL) >> 40)
                | (val >> 56);
            //return Unsafe.Read<ulong>(&val);
            return val;
        }

        public unsafe static ulong FlipNew(ulong val)
        {
            //ulong val = 0;
            //Unsafe.Write(&val, value);
            val = ((val & 0xFFFF0000FFFF0000UL) >> 16) | ((val & 0x0000FFFF0000FFFFUL) << 16);
            val = ((val >> 8) & 0xFF00FF00FF00FF00UL) | ((val << 8) & 0x00FF00FF00FF00FFUL);
            val = (val << 32) | (val >> 32);
            //return Unsafe.Read<ulong>(&val);
            return val;
        }