Note that if we had more informative events (including in this case what property had changed and what the previous value was) we wouldn't need to do extra work when reassigning a feature id.

By more informative events I mean something like our `beforepropertychange` and `propertychange` events - though these are still cumbersome (see [`Object.observe`](http://wiki.ecmascript.org/doku.php?id=harmony:observe_api_usage) for a more useful API).  In my opinion, it is a somewhat awkward implementation detail that some changes fire the generic `change` type and others fire the more informative `beforepropertychange` and `propertychange` events.  It would be nice to discuss harmonizing things before 3.0 final.