ViewSheet number

Hi

I tried to change a sheet number via APi through this code:

 Transaction t = new Transaction(m_doc, "Do it");
            t.Start();
            FilteredElementCollector sheets = new FilteredElementCollector(m_doc).OfClass(typeof(ViewSheet));
            foreach (ViewSheet sht in sheets)
            {
                if (sht.SheetNumber.StartsWith("L20-")) sht.SheetNumber = sht.SheetNumber.Replace("L20-", "A");
            }
t.Commit();

and it successfully did the job, unfortunatly it didnot change the SheetView name, Although Changing Sheetnumber through UI is auto change View name. do i miss something?