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VTT Subtitles Do Not Display Closed Caption Button in Chrome, Firefox, and Opera

Created by: chrishalebarnes

Environment

The MPD passes the DASH-IF Conformance Tool on http://dashif.org/conformance.html
The stream has correct Access-Control-Allow-Origin headers (CORS)
There are no network errors such as 404s in the browser console when trying to play the stream
The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ - Note: The wiki mentions VTT captions with this video, but it displays the same behavior, and doesn't play on Safari for some reason.
The issue occurs in the latest reference client on http://dashif.org/reference/players/javascript/ and not just on my page

Link to playable MPD file
Dash.js version: 2.5.0
Browser name/version: Chrome, Firefox, Opera display the issue, Safari does not
OS name/version: macOS Sierra

Observed behaviour

Chrome, Firefox and Opera do not display the closed caption button to switch between tracks/languages.

Safari displays the closed caption button as expected.

Chrome: Firefox:

Opera:

Finally, Safari seems to be ok:

See this Codepen

Not sure if this is a bug or if I have to flip on some setting, thanks for your help!