Renaming sheets from Format->Sheet->Rename is not available under Maemo 5 port, because it's using statusbar to change a sheet name. If you want to rename a sheet, you should open the Sheet Manager (Ctrl+M), double tap on a fourth column of the sheet table (it will be a empty space next to "Sheet1" or similar), type a new name for a sheet, tap on sth else in the table and click the "Apply Name Changes" button.