When RadTextBox is bound to a column (GridViewTextBoxColumn) in RadGridVIew it shows the current cell value. But once new row is added the value in the text box does not clear. Instead the last value stays. In case you add another row the value is being cleared.
RadGridView has two modes of adding new rows. The AddNewBoundRowBeforeEdit property determines the behavior of the new row. If one wants the same behavior as the standard grid control he or she should set the AddNewBoundRowBeforeEdit property to true. More information can be found in the online documentation http://www.telerik.com/help/winforms/gridview-rows-new-row.html