this is a known problem (having to do with the file name parsing - when folks rename file it causes problems amon other things) - the logic is being replaced with code that pulls details from specific tables within the backup instead of the file name itself.
in the meantime you can still download the older version of the MDB Viewer off the same COBRAS home page (there's a link to it in the nodes about the COBRAS backup editor) - it also allows for editing of alias/extensions, although not quite as slick.