Content property can only be set once

[JohnHardy]

When using the control I found I had to add the child items to a Items collection rather than following the example code listed on the website:

        <rm:RadialMenu IsOpen="True">
            <rm:RadialMenu.CentralItem>
                <rm:RadialMenuCentralItem>
                    <TextBlock>Close</TextBlock>
                </rm:RadialMenuCentralItem>
            </rm:RadialMenu.CentralItem>

            <rm:RadialMenu.Items>
                <rm:RadialMenuItem>
                    <TextBlock>A</TextBlock>
                </rm:RadialMenuItem>
                <rm:RadialMenuItem>
                    <TextBlock>B</TextBlock>
                </rm:RadialMenuItem>
            </rm:RadialMenu.Items>
            
        </rm:RadialMenu>

I'm running .NET 4.2. Is this behaviour expected?