See http://jsfiddle.net/69z2wepo/3887/ for example code.
When setting and removing focus from an empty <input /> field with some placeholder text, the onChange event is triggered for IE 11 (I have not tested older versions). It does not trigger for other browsers.
My current work-around is to test the value that was last passed to the input with what is returned by event.target.value, and only act if they are different, but it would be nice if React would not send the change-event in the first place.