Losing chr(13) when copy string to Rich Text Box

I have had some strange behaviour in a program I am moving from VB6 to vb.net and finally discovered that I am losing a character when I do the following:

Code:

---

Private Sub Form1_Load( ByVal sender As System.Object,  ByVal e As System.EventArgs) Handles MyBase.Load

  Dim intChr10  As Integer
  Dim intChr13  As Integer
  Dim intLength As Integer
  Dim strM      As String

  strM =        "Line 1" & vbCrLf
  strM = strM & "Line 2" & vbCrLf
  strM = strM & "Line 3" & vbCrLf
  strM = strM & "Line 4" & vbCrLf

  intChr10 = CountCharacter(strM, Chr(10))  ' = 4
  intChr13 = CountCharacter(strM, Chr(13))  ' = 4
  intLength = Len(strM)                    ' = 32

  RichTextBox1.Text = strM
  intLength = Len(RichTextBox1.Text)        ' = 28

  intChr10 = CountCharacter(CStr(RichTextBox1.Text), Chr(10))  ' = 4
  intChr13 = CountCharacter(CStr(RichTextBox1.Text), Chr(13))  ' = 0

End Sub

Private Function CountCharacter(strSample As String, ch As Char) As Integer
  Dim cnt As Integer = 0

  For Each c As Char In strSample
    If c = ch Then cnt += 1
  Next

  Return cnt
End Function

---

Specifically, copying the string to the RTB seems to change vbCrLf into vbLf ie it seems to lose Chr(13). Anybody understand this?

Many thanks ...