<p>To reproduce this major bug, </p> <p>1. Closed milestones must be hidden</p> <p>2. Add a new milestone</p> <p>3. Go to the parent milestone, for example, in our case a sprint was added to a release, when we open the release, all the previously closed sprints are unlinked (please see attachment). </p> <p>NOTE: In the planning view, if the closed milestones are displayed and you add a new milestone, the closed milestones are still there.</p>