App's title need to clear browser caches to take effect

After adding <title>{%title%}</title> in app.index_string, and assigned every app a title, it seems we need to clear browser caches by pressing ctrl+shift+r to see the title take effect. Is there any parameter I can add to make the title reload when navigating to the app? Thanks.

( I tried both @server.route("/apps/<path>") and callback to assign app.title. They really changed the titles, but the browser apparently remains the same title. )