El servicio de Windows cambia el comportamiento de la redirección de eco/secuencia en el archivo por lotes

Create a Windows batch file c:\test\first.bat:

@echo off
echo A
call second.bat < empty.txt
echo B
echo C

and two empty files c:\test\second.bat and c:\test\empty.txt (The same happens if they are not empty.)

Run first.bat. As expected the output is

A
B
C

Now, instead of running the batch file directly, create a C# command line application:

using System.Collections.Concurrent;
using System.Diagnostics;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var processInfo = new ProcessStartInfo("cmd.exe", @"/c c:\test\first.bat");
            processInfo.CreateNoWindow = true;
            processInfo.UseShellExecute = false;
            processInfo.RedirectStandardError = true;
            processInfo.RedirectStandardOutput = true;
            var process = new Process();
            process.EnableRaisingEvents = true;
            var log = new BlockingCollection<string>();
            process.OutputDataReceived += (sender, e) => log.Add(e.Data);
            process.Exited += (sender, e) =>
            {
                process.Dispose();
                File.WriteAllText(@"c:\test\log.txt", string.Join("\n", log));
            };
            process.StartInfo = processInfo;
            process.Start();
            process.BeginOutputReadLine();
            process.BeginErrorReadLine();

            process.WaitForExit();
        }
    }
}

Again, as expected the file c:\test\log.txt is created and contains

A
B
C

Now, instead of a command line application, create a Windows Service:

using System.Collections.Concurrent;
using System.Diagnostics;
using System.IO;
using System.ServiceProcess;

namespace WindowsService1
{
    public partial class Service1 : ServiceBase
    {
        public Service1()
        {
            InitializeComponent();
            this.CanStop = true;
        }

        protected override void OnStart(string[] args)
        {
            var processInfo = new ProcessStartInfo("cmd.exe", @"/c c:\test\first.bat");
            processInfo.CreateNoWindow = true;
            processInfo.UseShellExecute = false;
            processInfo.RedirectStandardError = true;
            processInfo.RedirectStandardOutput = true;
            var process = new Process();
            process.EnableRaisingEvents = true;
            var log = new BlockingCollection<string>();
            process.OutputDataReceived += (sender, e) => log.Add(e.Data);
            process.Exited += (sender, e) =>
            {
                process.Dispose();
                File.WriteAllText(@"c:\test\slog.txt", string.Join("\n", log));
            };
            process.StartInfo = processInfo;
            process.Start();
            process.BeginOutputReadLine();
            process.BeginErrorReadLine();
        }

        protected override void OnStop()
        {
        }
    }
}

Install and start the service (allow the required permissions to all related files). (It does not seem to matter which account (User, Local Service, Local System ...) is used for the service.)

Again the file c:\test\slog.txt is created, but now it contains:

A
echo B
B
echo C
C

¿Por qué?

(Maybe related: If there is no newline character after "echo C" in first.bat, the slog.txt contains:

A
echo B
B
more?

Why?)