If the event buffer fills up, can setTimeout()'s fail to fire?

That's interesting - I guess it is possible that Espruino can get totally overwhelmed. The code looks a bit like this:

function onIdle() {
  while (hasEvent) handleEvent();
  while (hasTimer) handleTimer();
}

So if you get so many input events that the queue can never get emptied, it'll get stuck. I'll file a bug for this and will fix it for 1v72 - probably doing something like:

function onIdle() {
  var howMany = getHowManyEvents();
  while (howMany--) handleEvent();
  while (hasTimer) handleTimer();
}