PopupGallery categories dont appper when ItemsSource is binded to an observable collection

Hello!

I am confused with appearance of category headers in PopupGallery. When items collection is explicitly defined in XAML with ‘ribbon:PopupGallery.Category’ property on each item, the category headers are shown. When I bind CategorizedItemsSource to an observable collection which contains data objects (inherited from DependencyObject), the category header are missed, despite of that I set the attached Category property in object’s constructor, e.g.:

this.SetValue(PopupGallery.CategoryProperty,”GroupA”);

I also tried approach with binding the PopupGallery to a delegate property with:

ItemCategoryDelegate="{Binding MyItemCategoryDelegate,RelativeSource={RelativeSource Mode=FindAncestor, 
AncestorType={x:Type Window}}}"

Again, when CategorizedItemsSource is set to a XAML list, my static delegate method is called normally. When I change binding to the observable collection, the method is not called at all (it does not hit a breakpoint) and categories are ignored.

Can you provide an example how to make up categories with binding to an observable collection?

Thank you in advance!

Ilia