If openam.session.persist_am_cookie is set to true then the iPlanetDirectoryPro cookie is made a persistent cookie, otherwise it remains as a session cookie.
The DAS sets the cookie in the LoginViewBean setCookie method; but the setCookie method will always make the cookie persistent and this method is used to set the AMAuthCookie as well as the iPlanetDirectoryPro cookie.
The setCookie method in the LoginViewBean should check ac.getStatus() == AuthContext.Status.SUCCESS and if it is set the cookie to persistent if enabled. Otherwise leave it as a session cookie.
This fix should go in the LoginViewBean in the DAS and the normal UI.