OAM 11.1.2.1 login directly using custom login page

Dears,

We are running OAM 11.1.2.1 on Solaris 11. We have Webcenter portal & ATG applications deployed on Weblogic servers 10.3.6, also on Solaris 11.

We configured some protected resources on OAM, for both Portal & ATG apps, using an external challenge/login page. SSO is working fine for both apps. When we try to access a protected resource, we're successfully redirected to our custom login page, enter a valid user/password, then redirected back to our originally requested resource.

Until now, everything looks fine. Our problem here may be described as follows:

1- If a user logged in successfully, then just after logging in he pressed Back is his browser, the login page is displayed again. If he then enters user/password again, OAM error page is displayed, and the following error is recorded in the log: "<Warning> <oracle.oam.controller> <OAM-02074> <Error while checking if the resource null is protected or not.>". Please note that in this scenario, the parameters passed through by OAM were maintained in the URL _like 'resource_url' for example_, so theoretically a target URL is present.