The solution to this problem is to refetch data from the DB again to the DataSource to which the grid is connected to. In this case, the grid will know that data was changed and refreshes its contents.
Also, I suggest that you set the breakpoint in the event handler you posted and make certain that the actual modified data is fetched from the DB.
Also, it is more correct to use the following code:
if not e.Page Is Nothing andalso e.Page.SelectedTabPageIndex = 3 Then
...