prevent duplicate captions when YouTube video has yt:cc=on

If YouTube video has yt:cc=on attribute when embedding the video in html5 mode, captions loads by default and can't be disabled. If you add caption via jwplayer there will be duplicate captions.
example:
http://jsfiddle.net/UAR3U/25/show/
YouTube captions can only disable via javascript API easily:
player.unloadModule("captions");