This is annoying. I have gotten into the habit of holding down then shift key when hitting return to avoid this. What happens when you hit <RETURN> is one of those dividing issues. 50% of people want a new line and 50% want it to submit.
That is not what he is talking about. Japanese language requires a conversion process when entering kanji and other characters. We type inline and use the return key to finalize the conversion process. The Return key is used to confirm the text input, not to break lines. This return input should not activate the subumit button, but Firefly does. This should be a bug.