Right now, users can add metrics to the project activity to create graphs. If a user types a non-existing (or unavailable) metric key, it will fail the WS. But because all parameters are stored in session storage, there's no way to fix this; the user will be redirected to the Overview page. Clearing the session storage fixes this.
The reason this is stored in session storage is to show the same metrics on the Overview page (activity graph on the right).