Shibboleth plugin overrides logout redirect url even user did not log in through Shibboleth

When I have both manual accounts and Shibboleth authentication enabled, if I log in through a manual account in Moodle and then log out, I got redirected to the Shibboleth logout page. I only want to be redirected to this url when I logged in through Shibboleth, which will completely log me out of my idp. But if I log in from a manual account, I want to be redirected to the default logout page when logout.

I guess one way to fix this is to change logoutpage_hook() in "auth/shibboleth/auth.php" to check for $USER->auth. Only override the global variable $redirect when $USER->auth == "shibboleth".

Hope this will make it to the core soon. Thanks!