Its possible to add a release to the user story map, place features against a master feature and release.
If you then remove the release from the user story map and add it back again, all the features that are still against the release don't show up in the user story map.
This is quite frustrating as its quite easy to accidentally remove a release from the map. And a lot of work is lost.
Thank you for your idea. It is currently possible to add both the release and features back to the map using the Add existing records section to the right of the map.