If AllowMultiRowSelection="True" in a grid, selecting individual rows by clicking on them unselects all previously selected rows. In a non mobile environment this is ok since the user has access to the CTRl or SHIFT keys to select multiple rows. However, in a touch environment, they don't. It is true they can click on the client select column to select multiple rows, but again, clicking on the row itself to select it, unselects all previously selected rows.