When GridViewClipboardPasteMode is set to AllSelectedCells and a single clipboard value is pasted into more than one selected cell, RadGridView updates the cell values but does not re-evaluate live grouping for the edited items - rows remain under their previous group header until an explicit Rebind()/refresh. 

Pasting into a single cell at a time re-groups correctly.

To work this around, call the CommitEdit and EditItem methods of RadGridView for each row data item in which data was pasted. You can do that in the Pasted event handler:

 private void RadGridView_Pasted(object sender, RadRoutedEventArgs e)
 {
     var editableView = (IEditableCollectionView)this.gridView.Items;
     var affectedItems = this.gridView.SelectedCells.Select(c => c.Item).Distinct().ToList();

     foreach (var item in affectedItems)
     {
         editableView.EditItem(item);
         editableView.CommitEdit();
     }
 }