How do Effective Dates work in the P3403 Application

We are trying to use Effective dates to update information in the F3403 table via the P3403 application.  We ended the effective date of the current record and then tried to add a new record with new non-overlapping effective dates.  When we do that, we receive a duplicate entry error.  It seem the system will only allow you to update the existing record and then it does not maintain the history.  Has anyone else experienced this?  Is it a bug?  It seems that if you have associated effective dates you should be able to use them to track history.