Shib session question

[Mike Flynn]

I have a new IDP trying to connect to me and we are having a little issue.
Works fine when the first SAML response is sent to our service, but when the user returns to their application, switches users and sends us a new SAML assertion, their original session seems to persist and the new response is ignored.  This results in the second user utilizing the first user's token.  SAML response IDs and user tokens are different in the responses.
Clearly the issue is with the iDP since I have a zillion other idps that connect fine. 

Any guidance here would be greatly appreciated.

Thanks so much!
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