To reproduce:
1. Set the RadGridView.MultiSelect property to true.
2. Set the SelectionMode = Telerik.WinControls.UI.GridViewSelectionMode.CellSelect
3. When you select multiple cells, the SelectedCells collection stores the cells in reversed order instead of keeping the selection order. Compared to GridViewSelectionMode.FullRowSelect, this behavior is different.

Workaround: iterate the SelectedCells collection in reversed order