Upgrading to .NET 4.5: An ItemsControl is inconsistent with its items source

I'm building an application, which uses many ItemControls(datagrids and listviews). In order to easily update these lists from background threads I used this extension to ObservableCollections, which has worked fine:

http://geekswithblogs.net/NewThingsILearned/archive/2008/01/16/have-worker-thread-update-observablecollection-that-is-bound-to-a.aspx

Today I installed VS12(which in turn installed .NET 4.5), as I want to use a component which is written for .NET 4.5. Before even upgrading my project to .NET 4.5 (from 4.0), my datagrid started throwing InvalidOperationException when updated from a workerthread. Exception message:

This exception was thrown because the generator for control 'System.Windows.Controls.DataGrid Items.Count:5' with name '(unnamed)' has received sequence of CollectionChanged events that do not agree with the current state of the Items collection. The following differences were detected: Accumulated count 4 is different from actual count 5. [Accumulated count is (Count at last Reset + #Adds - #Removes since last Reset).]

Repro code:

XAML:

<Window x:Class="Test1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
   <Grid>
      <DataGrid ItemsSource="{Binding Items, Mode=OneTime}" PresentationTraceSources.TraceLevel="High"/>       
   </Grid>
</Window>

Code:

public partial class MainWindow : Window
{
    public ExtendedObservableCollection<int> Items { get; private set; }

    public MainWindow()
    {
        InitializeComponent();
        Items = new ExtendedObservableCollection<int>();
        D