When the grid is being paged, it is actually aware of the current page only. The RadGridView simply "knows" that someone is changing its ItemsSource, which is the new page. It does not know how many pages are there and it also does not know about all the other items not displayed on the current page.
You could remember the selection and set the SelectedItems once a page is navigated
to, however, RadGridView.SelectionItems collection can only hold the selected items on the current page.
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