If ItemsSource is binded to a PagedCollectionView and this collection gets filtered, SelectedItem doesn't update. This problem is caused from the same issue with ListBox control.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.