Swift: Memory leak when storing enum in class

AppDelegate.swift

//
//  AppDelegate.swift
//  LeakCheck
//
//  Created by Alex Robinson on 15/2/17.
//  Copyright © 2017 Alex Robinson. All rights reserved.
//

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    var section = Section()

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool { return true }
    func applicationWillResignActive(_ application: UIApplication) { }
    func applicationDidEnterBackground(_ application: UIApplication) { }
    func applicationWillEnterForeground(_ application: UIApplication) { }
    func applicationDidBecomeActive(_ application: UIApplication) { }
    func applicationWillTerminate(_ application: UIApplication) { }
}

struct Item { }

enum DownloadStatus {
    case unknown, success, failure
}

class ItemList {
    var downloadStatus: DownloadStatus = .unknown // This is the problematic property. Comment it out, or change it to a Bool and there is no leak.
    var contents: [Item]
    init(contents: [Item]) {
        self.contents = contents
    }
}

class Section {
    var lists: [ItemList] = []

    init() {
        populateData()
    }

    func populateData() {

        /*
         A `_ContiguousArrayStorage<Item>` is leaked for each `ItemList`.

         Leak Checks Instrument output:

         Leaked Object	#	Address	Size	Responsible Library	Responsible Frame
         _ContiguousArrayStorage<Item>	1	0x17004d800	48 Bytes	libswiftCore.dylib	swift_slowAlloc
         _ContiguousArrayStorage<Item>	1	0x17004dcb0	48 Bytes	libswiftCore.dylib	swift_slowAlloc
         _ContiguousArrayStorage<Item>	1	0x17004db60	48 Bytes	libswiftCore.dylib	swift_slowAlloc
         _ContiguousArrayStorage<Item>	1	0x17004dce0	48 Bytes	libswiftCore.dylib	swift_slowAlloc
         _ContiguousArrayStorage<Item>	1	0x17004de30	48 Bytes	libswiftCore.dylib	swift_slowAlloc

         */

        self.lists = [
            ItemList(contents: [Item()]),
            ItemList(contents: [Item(), Item()]),
            ItemList(contents: [Item(), Item(), Item()]),
            ItemList(contents: [Item(), Item(), Item(), Item()]),
            ItemList(contents: [Item(), Item(), Item(), Item(), Item()]),
        ]
    }
}

http://www.openradar.me/30549163