You mention that - when you use Case Manager you do not see the problem, however when you use the Case Worker you do. Can you please confirm that you are testing this by launching either portals from the same developer/admin accessgroup?
The reason why I am asking you the above is because in the very next statement you mention that when you tested with a user of accessgroup WorkUsers the same issue happens. So I am not convinced that ROLES on the accessgroup may be contributing to the problem here.
Is it possible for you to mock up this scenario in a sample ruleset that you can send us here, we can import it locally and verify/debug the same to take it further.
1) I'm actually launching from both scenarios, from admin/developer and from an user(which belongs to WorkUsers) created for this purpose in my current (and local) application. And for the WorkUser, the portal set was the case worker (not case manager).
2) I will create an mock environment asap and send it for you.