To reproduce: - Add grid with a DateTime column with default value "5/1/2014"; - Start the app and press the following keys one after another: 5/1/ - You will notice that the "1" is not replaced. Please note that the similar behavior occur when the year is entered (it does not match the default one). Workaround handle the key press for such cases manually: void radGridView1_CellEditorInitialized(object sender, GridViewCellEventArgs e) { RadDateTimeEditor ed = e.ActiveEditor as RadDateTimeEditor; RadDateTimeEditorElement el = ed.EditorElement as RadDateTimeEditorElement; el.KeyPress += el_KeyPress; } private void el_KeyPress(object sender, KeyPressEventArgs e) { RadDateTimeEditorElement el = (RadDateTimeEditorElement)sender; int day = el.Value.Value.Day; int key = -1; int.TryParse(e.KeyChar.ToString(), key); RadMaskedEditBoxElement element = el.TextBoxElement.TextBoxItem.Parent as RadMaskedEditBoxElement; MaskDateTimeProvider provider = element.Provider as MaskDateTimeProvider; if (provider.SelectedItemIndex == 2) { if (key > 0 & key <= 9) { if (el.TextBoxElement.TextBoxItem.SelectionLength != 0) { if (!booKeying) { dynamic NewValue = new DateTime(el.Value.Value.Year, el.Value.Value.Month, key); el.Value = NewValue; e.Handled = true; booKeying = true; } } } } }