WPF Usercontrol my Richtextbox is not importing the flowdocument properly

Hey guys,

I have created a usercontrol (and by created I mean ripped off wholesale from a much better coder than me) that is basically a mini word processor.  What I want to do is click on a richtextbox (hereinafter RTB) on my screen and then open the usercontrol and edit the text of that RTB.  I already have the code to break down the first RTB and copy the content of all the blocks.  I trigger an event to send the list of blocks over to the usercontrol where I form the flowdocument and set the usercontrol RTB.Document to the new flowdocument.  Here is the trigger function:

    Public Sub Import_Text_Event(B_Col As List(Of Block)) Handles frm.ExportText

        Dim flow As New FlowDocument

        For Each B As Block In B_Col
            flow.Blocks.Add(B)
        Next

        TextBox.Document = flow

    End Sub

Here 'TextBox' is the RTB that is set in the usercontrol.  The problem is that it doesn't update on the usercontrol instance on my active form.  I know that the flowdocument is being constructed properly.  I've checked during debugging and confirmed that all the blocks copy and are sent over in B_Col (listed above) and the 'TextBox.Document = flow' works in other paces.  I've used this format to tie two RTB's on the same page together so that the changes made in one are reflected in the other.  Am I going about this the wrong way?  I'm sending the flowdocument to the usercontrol class to make the update...is that not how this should work?  Should I be making the change on the controlling form?

Anyway, I'm still new to WPF and even newer to Usercontrols so anything you can give me will be appreciated!