After checking carefully the new version, it appears that Apple has changed completely the file format with the new iCal. It is now much more complicated than with the previous version... perhaps to force to have a .mac account.
During Leopard installation, the old Tiger iCal files are not deleted. It is them that you see within iCal but they are no longer used and then are not updated.
I cannot promise at that time to be able to find a way to render FTPiCal compatible with Leopard.
Sorry for that