After upgrading JoomSEF, the duplicate URLs have appeared, why is that?

If you have updated from previous major version, e.g. from 1.4.0 to 1.5.0, you may experience that some of the URLs are duplicated, even though they were okay previously. This may be caused because the format of SEF URLs stored in your database has changed and the new URLs are lokking slighly different than the old ones. In such case, if you do not want JoomSEF to regenerate them automatically (by either purging the existing one or deleting them manually) or if you have many customized URLs, you will need to use the JoomSEF DB upgrade script 1.5.0 to update the DB for you. Your are highly encouraged to backup your DB prior to doing this! After updating, the old URLs will have the same format as the new ones, so they will be matched correctly and no duplicates will appear.