Datagrid works different under .NET 4.0 and 4.5

After Update from .NET 4.0 to 4.5 I see only small black lines in my Datagrid.
I bind the Datagrid to a Datatable. It works fine under .NET 4.0.

The XAML and the Code behind:

<ListBoxName="DumpList"Grid.Row="2"Grid.Column="0"HorizontalContentAlignment="Stretch"ItemsSource="{Binding m_dump}"ScrollViewer.HorizontalScrollBarVisibility="Disabled"><ListBox.ItemTemplate><DataTemplate><Grid><Grid.RowDefinitions><RowDefinitionHeight="100"/></Grid.RowDefinitions><DataGridName="DumpGrid"Grid.Row="0"ItemsSource="{Binding}"AutoGenerateColumns="True"IsReadOnly="True"SelectionMode="Extended"HorizontalScrollBarVisibility="Visible"></DataGrid></Grid></DataTemplate></ListBox.ItemTemplate></ListBox>

privateObservableCollection<DataTable> _dump =newObservableCollection<DataTable>();publicObservableCollection<DataTable> m_dump{
        get{return _dump;}set{
            _dump = value;OnPropertyChanged("m_dump");}}

Where could be the Problem?