Use the following information to help trouble issues with the Single Sign-on applications.
Issue: If you have Single Logout (SLO) enabled in Salesforce, but you did not provide the logout URL in the Salesforce application configuration, Single Sign-on does not terminate the session to Salesforce when a user logs out of the Application portal.
Solution: If you enable Single Logout (SLO) in Salesforce, provide the logout URL. If you do not have SLO enabled in Salesforce, do not provide a logout URL during the configuration of the Salesforce application.