Shiny app with custom domain is in iframe, so how I control the page title?

I have a Shiny app, deployed under the Professional plan and with a custom domain in accordance with the instructions at Everything works fine - except that when viewing the app at the URL I want users to use, the webpage Title (coming from navbarPage(..., windowTitle =""), not that I think that matters) is not showing up in the browser tab. It works fine at the address, just not at the address I have set up.

Inspecting the source of the page shows that the probable reason is that page is actually an iframe pointing This isn't causing any problems (yet) other than this window title problem, so is there a way I can set the title of the page that is embedding my main location in an iframe?