User Story Map - Adding a release also adds the features in the release

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.