+++ This bug was initially created as a clone of Bug #14034 +++
The shibboleth authentication only support partial single sign out at the moment...
i.e. it supports it in one direction. We can submit a signout request to the IdP at koha logout time, but we are not yet listening to logouts on the shibboleth service.
I'm not even sure how well documented this feature is in the level above us, but I thought it worth noting here whilst I find time to work on it.