nested describe blocks are added last to the quick report display bar:
Have you looked at master at all? For 2.0 we should be more rigorous about when items get added in the new HtmlReporter.
That said, we don't have a spec for this particular behavior.
We've made a story in tracker for this here: https://www.pivotaltracker.com/story/show/58125418
We'll look at it again after 2.0