Binding and Async Operations

 have created a Window with a TextBlock inside. I have bound the Text property and everything works fine. BUT When I change the bounded property while inside a Task then nothing works!!

Do you know why?

Public Async Sub StartProgress()
    Try
       LoadingText = "text 1" 'Works perfect

       Dim fResult As Boolean = Await LoadModules()

       If Not fResult Then
          MessageBox.Show(Me.Error)
       End If

       m_oView.Close()
    Catch ex As Exception
       Msg_Err(ex)
    End Try
End Sub

Public Async Function LoadModules() As Task(Of Boolean)
    Try
        Await Task.Delay(3000)

        LoadingText = "text 2" 'Nothing Happens

        Await Task.Delay(5000)

        LoadingText = "complete" 'Nothing Happens

        Await Task.Delay(3000)

        Return True
    Catch ex As Exception
        Me.Error = ex.Message
        Return False
    End Try
   End Function

text 2 and 3 are never shown. If I change dynamically the Text of the textblcok(ex : m_oView.txtLoadingText.Text) It works fine(but it's mnot a solution)