现代用户界面 - 现代菜单不会显示链接内容

I´m writing a WPF application based on FirtsFloorSoftware Modern UI. I´m facing problems when I´m trying to show the content (UserControl) set with 'Source =' in a Link. To display the problem I have made a small separet app.I´m writing a WPF application based on FirtsFlo