If you add a new epic to a user task, the epic is put in unscheduled. If you now want to move that epic into a specific release, you can only do so, if it is possible to dock this epic in the top of that release or if it is possible to dock this epic just underneath the last epic in that release.
If you have many unscheduled epics or you have many releases you sometimes end up by moving the epic up many times, till you are able to put it where it belongs. It would be better if you could either drag the epic and being able to scroll or even better to have an option to set the release within the epic. At the moment the release is not editable within the epic.