One of the rules with Drupal.org hosted projects is to not introduce radical API changes (or depending on your understanding even new features) in point releases of stable branches of contributed modules, so you are supposed to open a new branch. The hell starts to break loose however, if you don't have an eye on what is actually happening in your branches. This happened to me and it affected the Drupal 6 translation efforts so it was just the right time yesterday to finally clean it up. Here's the story.
Drupal related posts by Gábor Hojtsy.