Angular ngModel directive binds to `this` instead of `$scope`

Statement: I have had this problem many times before and it always seems to be random.

Define Random: Random as in which properties it does this to, the result is reproducible between debugging sessions, and on multiple environments/browsers.

Behavior: My issue is the textarea with ng-model="sometext" is binding to this.sometext instead of $scope.sometext. When I enter "hello" into the textarea and place a breakpoint in chrome and inspect the value of $scope.sometext it is "" but when I inspect this.sometext it is "hello".

Background: All of the other properties (not shown for brevity) bind correctly to $scope but this specific one does not. I am not using controllerAs

Question: Why does this happen? and how do I fix it so it binds correctly to $scope instead of this

Code:

Controller:

1  angular.module 'myApp'
2  .controller 'HomeController', ($scope, Engine) ->
3    $scope.playButtonText = 'Play'
4    $scope.sometext = '' #<- Setting initial value
5
6    $scope.play = ->
7      if $scope.playButtonText is 'Play'
8        $scope.playButtonText = 'Stop'
9        promise = Engine.play $scope.sometext
10       if promise is false
11         $scope.playButtonText = 'Play'
12       else
13         promise.then ->
14           $scope.playButtonText = 'Play'
15     else $scope.playButtonText = 'Play'

View:

ion-view(title='My Title')
  ion-content
    h2(class='text-center') Enter text, choose playback, choose speed, and press play
    div(class='list')
      label(class='item item-input')
        # THIS TEXTAREA IS THE ONE
        textarea(placeholder='Enter some text to translate', ng-model='sometext')
    button(type='button', class='button button-full button-stable', ng-click='play()') {{playButtonText}}

Config:

angular.module('myApp', ['ionic'])
.config ($stateProvider, $urlRouterProvider) ->
  $stateProvider
  .state 'tab',
    url: "/tab"
    abstract: true,
    templateUrl: "templates/tabs.html"
  .state 'tab.home',
    url: '/home'
    views:
      'tab-home':
        templateUrl: 'templates/tab-home.html' #<- This is the view
        controller: 'HomeController' #<- This is the controller

  $urlRouterProvider.otherwise '/tab/home'

Engine:

angular.module 'morsecode'
.factory 'Engine', ($q) ->
  Engine = {}

  Engine.play = (text) ->
    if text.length is 0
      return false
    upper = text.toUpperCase()
    phrase = ''
    for letter in upper
      phrase += Engine.encodeLetter letter
    deferred = $q.defer()
    Engine.loop phrase, 0, Engine, deferred
    return deferred.promise

  return Engine

Not sure how the Engine code is relevant, but there it is (methods not related not included, it is rather complex with setTimeouts calling setTimeouts and lots of recursive code)

Debugging Image: