Highlight specific text while user is typing - vb.net

Question

I am writing a code that highlight the duplicate words in a text. The code is working well when I add a button and the user have to press on the button to check for duplicates.
But I want to make an auto-checking code. I set my code in a subroutine that Handles RichTextBox.TextChanged. The problem is the code selects the target word and highlight it but the selection remains so when a new letter is typed, it clear what has been highlighted.
Here is my code:
Private Sub RichTextBox_TextChanged(sender As Object, e As EventArgs) Handles RichTextBox.TextChanged
Try
Call duplicate_check()
Catch ex As Exception
MessageBox.Show("error in RichTextBox.TextChanged")
End Try
End Sub
duplicate check function:
Private Sub duplicate_check()
Try
' read line by line and get input
Dim LineByLineInput() As String = RichTextBox.Lines
Dim selectionStart, selectionLength As Integer
Dim i, j As Integer
For lineNumber = 0 To UBound(LineByLineInput)
selectionStart = 0
selectionLength = 0
'get index of first char index in the current line
Dim count As Integer = lineNumber
While count <> 0
selectionStart += RichTextBox.Lines(count - 1).Length + 1
count -= 1
End While
' get line as string
Dim line As String = RichTextBox.Lines(lineNumber)
' split line into array of strings
Dim input() As String = line.Split(" ")
'check for duplicates
i = 0
For j = i + 1 To UBound(input)
If input(i) = input(j) Then 'compare each 2 consecutive words if they are the same
selectionStart += input(i).Length + 1
selectionLength = input(i).Length
RichTextBox.SelectionStart = selectionStart
RichTextBox.SelectionLength = selectionLength
RichTextBox.SelectionBackColor = Color.Yellow
Else
selectionStart += input(i).Length + 1
End If
i += 1
Next
Next
Catch ex As Exception
MessageBox.Show("error duplicate_check()")
End Try
End Sub

Answer 1

After your duplicate_check call, have you tried to set the selection of the RichTextBox back to the old position ?
See below :
Private Sub RichTextBox1_TextChanged(sender As Object, e As System.EventArgs) Handles RichTextBox1.TextChanged
Try
' Get current position
Dim cur_pos As Integer = Me.RichTextBox.SelectionStart
Call duplicate_check()
' Set back to old position
Me.RichTextBox.SelectionStart = cur_pos
' Unselect what your sub duplicate_check has selected
Me.RichTextBox1.SelectionLength = 0
Catch ex As Exception
MessageBox.Show("error in RichTextBox.TextChanged")
End Try
End Sub
If this solution is good for you, you should change your duplicate_check Sub to make this change and not in the RichTextBox1_TextChanged Sub