WP-Cassify and iPhone/iPad access

Does anyone have an issue with users who access your WordPress site (using this plugin) and who are using iPhones and/or iPads? I am sending an email out from a site, and one of the users says that when he clicks the email link from his iPad and gets the CAS authentication screen, it does not allow him to open the site on his iPad, but it does on his iPhone, even though he authenticated on the iPad. Does that make sense? The device that authenticated does not allow him access, but if he then picks up his iPhone, he has access without authenticating. Any ideas?