New Post: CheckBoxComboBox - Problem with displaying Checks

Hello i have a urgent problem.

Im using component called CheckBoxComboBox from this toolkit in my project.

In my xaml i have this:

<Label x:Name="costCenterLabel" Content="Střediska" FontSize="17" FontWeight="Bold" Style="{StaticResource NormalLabel}" HorizontalAlignment="Left" Margin="186,10,-78,0" VerticalAlignment="Top" Width="93" Grid.Column="1"/>

<wpfTool:CheckComboBox x:Name="LoadingCenterComboBox" 
                         HorizontalAlignment="Center" 
                         VerticalAlignment="Center"   
                         FontWeight="Bold"
                         FontSize="14" 
                         DisplayMemberPath="LoadingCenterCode" 
                         ItemsSource="{Binding CostCenterFilter}"                          
                         SelectedItemsOverride="{Binding SelectedCenters, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"      
                         Margin="186,48,-156,27" Width="171" Grid.Column="1" Height="26">
            <wpfTool:CheckComboBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <UniformGrid Columns="4"/>
                </ItemsPanelTemplate>
            </wpfTool:CheckComboBox.ItemsPanel>
        </wpfTool:CheckComboBox>

I dont understand why , if i run application, in checkbox combobox is default selected value, but if i open it , in items source i dont see checked checkbox next to text.



In the image: The default cost center is displaying by display member path. But in the list its not checked. I dont know why. Any tips please? Thanks.