TwoWay binding in WPF

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WPF

Hi
I have a problem with getting twoway binding to work in WPF. I have

public List<AirlineMaintenanceMVVM> Maintenances { get; set; }

where AirlineMaintenanceMVVM is:

public class AirlineMaintenanceMVVM
{
    private MaintenanceCenterMVVM _selectedtype;
    public AirlinerMaintenanceType Type { get; set; }

    public MaintenanceCenterMVVM SelectedType
    {
        get
        {
            return this._selectedtype;
        }
        set
        {
            this._selectedtype = value;
            this.NotifyPropertyChanged("SelectedType");
        }
    }

    public ObservableCollection<MaintenanceCenterMVVM> Centers { get; set; }
    public AirlineMaintenanceMVVM(AirlinerMaintenanceType type, MaintenanceCenterMVVM selected, List<MaintenanceCenterMVVM> centers)
    {
        this.Type = type;
        this.Centers = new ObservableCollection<MaintenanceCenterMVVM>();

        centers.ForEach(c => this.Centers.Add(c));

        this.SelectedType = selected;
    }
    #region Public Events

    public event PropertyChangedEventHandler PropertyChanged;

    #endregion
    #region Methods

    private void NotifyPropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (null != handler)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    #endregion
}

In the xaml I have created a ListBox with a ComboBox inside, where the combo box binds to the elements and selected value from the MVVM-file. But eventhough I set the selected value when I create the MVVM-object, the value is not set when the combo box is shown:

 <ListBox ItemsSource="{Binding Maintenances}" removed="Transparent" BorderThickness="0" ItemContainerStyleSelector="{StaticResource ListBoxItemStyleSelector}" VerticalAlignment="Bottom">
   <ListBox.ItemTemplate>
      <DataTemplate>
         <WrapPanel>
            <TextBlock Text="{Binding Type.Name}" VerticalAlignment="Bottom" FontWeight="Bold" Width="100">
            </TextBlock>
            <ComboBox ItemsSource="{Binding Centers,Mode=OneTime}" Width="250"
               Style="{StaticResource ComboBoxTransparentStyle}"
               SelectedItem="{Binding SelectedType,Mode=TwoWay}"
               DisplayMemberPath="Name" SelectedValuePath="Name" />
         </WrapPanel>
      </DataTemplate>
   </ListBox.ItemTemplate>
</ListBox>

additional information copied from non-solution below
The selected value files in the mvvm object is correctly updated when I change the combobox