EWS Managed API Attachment - Properties of attchment to existing email are blank

Question

I am converting an existing application that uses Rebex as email provider to use EWS Managed API. My goal is to display a list of emails that have attachment via datagrid. I have successfully done that. However, when I select the email on the grid row to reply, all the attachment properties are null or have object is not reference. The only property that has value is the Name. For example, Content, ContentID, ContentLocation, ContentType are all blank.

Am I missing something? Below is my code to create a list of attachment:

Private Sub AddParentAttachments()
   For Each att As Attachment In _parentMailMessage.Attachments
    Dim item As IMailAttachment = Nothing
    item = New EwsMailAttachment(att)
    Me.Add(item)
  Next
End Sub