Only save category ids

assets/javascripts/wizard/components/wizard-field-category.js.es6

@@ -0,0 +1,9 @@
+import { observes } from 'ember-addons/ember-computed-decorators';
+
+export default Ember.Component.extend({
+  @observes('categories')
+  setValue() {
+    const categories = this.get('categories');
+    this.set('field.value', categories.map(c => c.id));
+  }
+});

assets/javascripts/wizard/templates/components/wizard-field-category.hbs

@@ -1,2 +1,2 @@
-{{category-selector categories=field.value maximum=field.limit}}
+{{category-selector categories=categories maximum=field.limit}}