Xcode6-beta crash on swift code

crash.playground

// Copy paste this in your playground
// sent at rdar://17316238

import Cocoa

var date_string = "2014/06/14 20:05:13 +0000"
var rfc3339DateFormatter = NSDateFormatter()
rfc3339DateFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
rfc3339DateFormatter.dateFormat = "yyyy/MM/dd HH:mm:ss Z"
rfc3339DateFormatter.timeZone = NSTimeZone(forSecondsFromGMT: 0)

// Working
rfc3339DateFormatter.dateFromString(date_string)

var options = Dictionary<String, AnyObject>()
options["send_at"] = date_string

// Working
var send_at = options["send_at"] as String!
rfc3339DateFormatter.dateFromString(send_at)

// Uncomment this for crashing xcode
// rfc3339DateFormatter.dateFromString(options["send_at"] as String!)