Backtracking re-render strange behavior

components.address-detail.js

import Ember from 'ember';
const {isBlank, set, computed} = Ember;

export default Ember.Component.extend({
    errors:Ember.computed('address.city','address.street', function() {
    let result = {};
    
    if (isBlank(this.get('address.street'))) {
        set(result, 'street', 'Street cannot be empty');
    }
    
    if (isBlank(this.get('address.city'))) {
        set(result, 'city', 'City cannot be empty');
    }
      
    this.get('onerrorraised')(result);
    
    return result;
  }),
});

components.error-displayer.js

import Ember from 'ember';

let ErrorDisplayer = Ember.Component.extend({
});

ErrorDisplayer.reopenClass({positionalParams: ['component', 'property']});

export default ErrorDisplayer;

components.person-detail.js

import Ember from 'ember';
const {isBlank, set, computed} = Ember;

export default Ember.Component.extend({  
  errors:computed('person.name','person.surname', 'externalError', function() {
    let result = {};
    
    if (isBlank(this.get('person.name'))) {
        set(result, 'name', 'Name cannot be empty');
    }
    
    if (isBlank(this.get('person.surname'))) {
        set(result, 'surname', 'Surname cannot be empty');
    }
    
    result = Ember.merge(result, this.get('externalError'));
    
    this.get('onerrorraised')(result);
    
    return result;
  }),
  
  actions: {    
    onexternalerrorraised(error) {
      this.set('externalError', error);
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  item: Ember.Object.create({address:{}}),
  isValid:Ember.computed('errors', function(){
    return Object.keys(this.get('errors')).length === 0;
  }),
});

helpers.error-formatter.js

import Ember from 'ember';

export function errorFormatter(params/*, hash*/) {
  let validatable = params[0];
  let property = params[1];
  return Ember.Object.create({
    validatable: validatable,
    //error: Ember.computed.alias(`validatable.errors.${property}`)
    errorBinding:`validatable.errors.${property}`
  });
}

export default Ember.Helper.helper(errorFormatter); 

templates.application.hbs

{{#person-detail person=item onerrorraised=(action (mut errors)) as |h|}}
	{{address-detail address=item.address onerrorraised=h.onexternalerrorraised}}
{{/person-detail}}

<br>
Is form valid: {{isValid}}

templates.components.address-detail.hbs

  <b>Address</b><br>
  Street: <input value={{address.street}} oninput={{action (mut address.street) value="target.value"}}>
  {{error-displayer this 'street'}}
  City: <input value={{address.city}} oninput={{action (mut address.city) value="target.value" }}>
  {{error-displayer this 'city'}}

templates.components.error-displayer.hbs

<span style="color:red">{{get (error-formatter component property) 'error'}}
</span><br>

templates.components.person-detail.hbs

<div style="border-style: solid; border-width: 1px;">
  <b>Person</b><br>
  Name: <input value={{person.name}} oninput={{action (mut person.name) value="target.value"}}>
  {{error-displayer this 'name'}}
  Surname: <input value={{person.surname}} oninput={{action (mut person.surname) value="target.value" }}>
  {{error-displayer this 'surname'}}
  {{yield (hash onexternalerrorraised=(action 'onexternalerrorraised'))}}
</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": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}