UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:48.0) Gecko/20100101 Firefox/48.0

Steps to reproduce the problem:
var u = new SpeechSynthesisUtterance('가나다라마바사아자차카타파하가나다라마바사아자차카타파하');
u.lang = 'ko-KR';
speechSynthesis.speak(u);
u.onstart = () => setTimeout(() => speechSynthesis.pause(), 1000);

What is the expected behavior?

What went wrong?
The above code does not paused until speaking all text. I think it is because the text does not have a punctuation marks. It's not a big problem, because I can know when it paused via onpause callback.

The real problem is it makes SpeechSynthesis broken. The above code makes the state of speechSynthesis be {pending: false, speaking: false, paused: true}, and it cannot be resumed even I manually run speechSynthesis.resume().

speechSynthesis.speak(another utterance) changes speaking flag to true and paused flag to false, but it makes no sounds just changes the state.

Did this work before? No 

Chrome version: 46.0.2460.0  Channel: dev
OS Version: 10.0
Flash Version: