Make the method handle both the MouseDown() and MouseMove() events like this:
Private Sub tbTest_MovePointer(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles tbTest.MouseDown, tbTest.MouseMove
If e.Button = Windows.Forms.MouseButtons.Left Then
Dim dblValue As Double
'Jump to the clicked location, bug FIX.
dblValue = (Convert.ToDouble(e.X) / Convert.ToDouble(tbTest.Width)) * (tbTest.Maximum - tbTest.Minimum)
tbTest.Value = Convert.ToInt32(dblValue)
End If
End Sub
*Note the multiple events listed after the Handles
keyword at the end of the first line. I also added a check to ensure the left mouse button is down.