串行端口拆分数据

在我的代码中，我发送Resume和Left，但由于某种原因，文本被拆分为这样：

[COM6] Pause
[COM6] Re
[COM6] sume
[COM6] 
[COM6] Le
[COM6] ft

这是我的代码

    var mySerialPort = new SerialPort
                {
                    BaudRate = int.Parse(nsComboBox1.Items[nsComboBox1.SelectedIndex].ToString()),
                    PortName = nsComboBox2.Items[nsComboBox2.SelectedIndex].ToString(),
                    ReadTimeout = 500,
                    ReadBufferSize = 1024,
                    Parity = Parity.Space,
                    StopBits = StopBits.One
                };
                mySerialPort.Open();
                mySerialPort.DataReceived +=
                    (o, args) =>
                    {
                        string s = mySerialPort.ReadExisting();
                        textBox1.Invoke(
                            new MethodInvoker(() => textBox1.Text += string.Format("[{0}] {1}", mySerialPort.PortName,
                                s) + Environment.NewLine));
//removed the rest for being irrelevant
                    };

我想这是因为我的选择，但我如何才能避免拆分文本？