proxying solution

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  userService: Ember.inject.service('user'),
  userController: Ember.inject.controller('user'),
  actions: {
    incrementController() {
      this.incrementProperty('userController.counter', 1);
    },
    decrementController() {
      this.decrementProperty('userController.counter', 1);
    },
    incrementService() {
      this.incrementProperty('userService.counter', 1);
    },
    decrementService() {
      this.decrementProperty('userService.counter', 1);
    },
    incrementServiceAlias() {
      this.incrementProperty('userService.counterAlias', 1);
    },
    decrementServiceAlias() {
      this.decrementProperty('userService.counterAlias', 1);
    },
  }
});

controllers.user.js

import Ember from 'ember';

export default Ember.Controller.extend({
  counter: 1,
});

mixins.proxy.js

import Em from 'ember';

export default Em.Mixin.create({
    unknownProperty: function(key) {
        return this.get('proxy').get(key);
    },
    init() {
        this._super(...arguments);
        var controller = this.get('proxy');
        for (var method in controller) {
            if (typeof controller[method] === 'function') {
                if (!this[method]) {
                    this.proxyMethod(method);
                }
            }
        }
    },
    proxyMethod: function(method) {
        this[method] = function() {
            var controller = this.get('proxy');
            return controller[method](...arguments);
        };
    },
});

services.user.js

import Ember from 'ember';
import ProxyMixin from '../mixins/proxy';

export default Ember.Controller.extend(ProxyMixin, {
  proxy: Ember.computed(function() {
        return this.container.lookup('controller:user');
  }),
  counterAlias: Ember.computed.alias('proxy.counter'),
});

templates.application.hbs

<h1>Proxy Mixin Bugs</h1>

<h2>Counter</h2>
<p>userController.counter: {{userController.counter}}</p>
<p>userService.counter: {{userService.counter}}</p>
<p>userService.counterAlias: {{userService.counterAlias}}</p>

<h3>User controller counter directly</h3>
<div>
<button {{action 'incrementController'}}>Increment</button>
<button {{action 'decrementController'}}>Decrement</button>
</div>

<h3>User service proxy to user controller</h3>
<div>
<button {{action 'incrementService'}}>Increment</button>
<button {{action 'decrementService'}}>Decrement</button>
</div>

<h3>User service alias to user controller</h3>
<div>
<button {{action 'incrementServiceAlias'}}>Increment</button>
<button {{action 'decrementServiceAlias'}}>Decrement</button>
</div>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "1.13.13",
    "ember-template-compiler": "1.13.13",
    "ember-testing": "1.13.13"
  },
  "addons": {
    "ember-data": "1.13.15"
  }
}