Several of the developers at the yt workshop are reclassifying the bitbucket issues to better "tag" them for future handling. We decided to use the "Milestone" field as a way of triaging these into several categories: easy, moderate, difficult, longterm, and waiting for future development. As part of this, we (I) made the dubious decision to remove the previous numbered milestones because they were redundant with version as we had been using them. This has resulted in a HUGE number of emails to the list for all of the milestone modifications, which you have undoubtedly received. For that I want to personally apologize, since we were unaware this would be the behavior even on closed tickets.
I hope these new milestones will be useful in the future, and again I'm sorry for all of the spam.