4.8.10.12.1 Text track model http://www.whatwg.org/specs/web-apps/current-work/#text-track-cue-active-flag The active flag … The user agent must synchronously unset this flag whenever the text track cue is removed from its text track's text track list of cues; whenever the text track itself is removed from its media element's list of text tracks or has its text track mode changed to disabled; and whenever the media element's readyState is changed back to HAVE_NOTHING. When the flag is unset in this way for one or more cues in text tracks that were showing or showing by default prior to the relevant incident, the user agent must, after having unset the flag for all the affected cues, apply the rules for updating the text track rendering of those text tracks. For example, for text tracks based on WebVTT, the rules for updating the display of WebVTT text tracks.