Requirements for Global Logout to work

• Clients which are being used for both the service providers should be in the same realm.
• When you log out from IdP, do you see a request being fired to logout from each of the service providers? I believe in your case, it is not calling Logout URL for your SP. That needs to be configured at a client level.
• If logout URL for SP is being called and if even then you are logged into your SP, then it means that SP has some issues in the implementation of Log out.

When you logout from SP first in that case your SP is sending logout request to IdP and that's why you are being logged out from IdP as well as SP. But on the other case, I believe Logout URL is not being called (which could be due to missing configuration in the client).

Can you post a screenshot of the configuration to help you better?