Word VBA Document_Open causes document to be flagged modified

Question

I have a Word 2010 (.docm) document and the following VBA code (under Project - Microsoft Word Objects - ThisDocument):

Private Sub Document_Open()
    Dim docTitle As String
    docTitle = BuiltInDocumentProperties("Title")
End Sub

Now if i only open the document and close it again Word asks me if i want to save the document. Why does word think that my document has changed, and what can i do to prevent this from happening? Thanks