Swift Interpolated String memory leak

AppDelegate.swift

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        
        // Instruments shows a memory leak here
        print("The number of the counting shall be \(3)")
        
        // but not here
        //print("The number of the counting shall be " + 3.description)
        
        if let widget = store.value.currentWidget {
            print(widget.widgetID)
        }

        return true
    }
}

Models.swift

import Foundation

struct Doodad {
    var doodadID: String
    var name: String
}

struct Widget {
    var widgetID: String
    var doodad: Doodad
    var startDate: NSDate
    var endDate: NSDate?
    var prop1: String?
    var prop2: String?
    var prop3: [String]
    var prop4: [String]
    var prop5: [String]
    var prop6: Double
    var prop7: NSDate?
}

enum NavigationState {
    case Main
    case Compare(Widget, Widget)
}

struct AppState {
    var navigationState: NavigationState = .Main
    var widgets = [Widget]()
    var prop1: [String] = []
    var prop2: String?
    
    init(widget: Widget) {
        widgets = [widget]
    }
    
    var currentWidget: Widget? {
        return widgets.filter { $0.endDate == nil }
            .sort { $0.0.startDate.compare($0.1.startDate) == .OrderedDescending }
            .first
    }
}

class Store<T> {
    var value: T
    
    init(_ initial: T) {
        value = initial
    }
}

let widget = Widget(widgetID: "sdfg", doodad: Doodad(doodadID: "8765", name: "jhg"), startDate: NSDate(), endDate: nil, prop1: nil, prop2: nil, prop3: [], prop4: [], prop5: [] , prop6: 10, prop7: nil)

let appState = AppState(widget: widget)
let store = Store<AppState>(appState)

Repro case for memory leak when using interpolated strings, vs no memory leak for concatenating.

It appears to be somehow related to assigning largish value types within the same scope. I’ve done my best to shrink the example down.

Note the type declarations need to be in a separate file, and optimisation set to 'fast' without -whole-module-optimization

I suffered from NSZombies when interpolating as well. Didn't check leaks, though. Maybe related?
https://gist.github.com/DivineDominion/c069c8d3d38d7cb880b5354524acf579

http://openradar.appspot.com/26349281