I have single sign on working beautifully, but single sign-out is not working.
The scenario is like this:
I had the same problem. We had a java and a php client. When I went to http://mycasserver/logout
only the java client logged out.
For the single sign out to work in the php client, you have to change:
phpCAS::handleLogoutRequests();
for
phpCAS::handleLogoutRequests(false);
And Voila! Refer to the documentation at phpCAS examples