It may be just my machine but it only appears to happen on the forum post message/reply page.
I'll respond to a question and the entry page will come up, can select quote and the original question will appear as a quote. Start typing an answer and hit enter to get a new line and the message gets sent. Appears to happen randomly. Quite often if I mistype and hit backspace a couple of times its sends.
I have to believe it's something on the page that is running real slow and finally completes as I'm in the middle of typing.