The issue reproduces in the following situation.
- The selection mode is Extended and the selection unit is Mixed.
- Multiple rows are selected.
- Cells of the selected rows are updated.
- The column of the updated cells is previously sorted (before the update of the cell values).
- DataTable is used to populate the RadGridView control.
To work this around set the SelectionUnit property of RadGridView to FullRow or use a collection type like ObservableCollection<T> instead of a DataTable.