Find category through ajax using ElementCriteriaModel

Question

I'm trying to run a controller action with ajax in a new plugin I'm making. The action needs to return all categories from a group, so nothing impossible here.

When I run the actionUrl in the browser I get the wanted result: an array with the titles of all categories in a group.

But when I call this action while using ajax it results in an empty array.

Ajax call

 $.ajax({
        url: Craft.getActionUrl('AddEntriesFilter/Index/GetCategories'),
        context: document.body,
        success: function(response) {
            console.log(response);
        }
});

Action in controller

public function actionGetCategories()
{
    $criteria = craft()->elements->getCriteria(ElementType::Category);
    $criteria->group = 'myCategoryHandle';

    $cats = $criteria->find();

    $regions = array();
    foreach ($cats as $cat)
    {
        $regions[] = $cat->title;
    }

     $this->returnJson($regions);
}

To test this, I tried to Craft::dd($cats); and this is already empty.

I also tried to Craft::dd($criteria->count()); and this also gives different results in the ajax call and in the browser. The ajax call returns 0 and the browser returns the wanted result.

After logging the attributes of $criteria I discovered $criteria->find()is adding a relatedTo attribute. It only does this when running it through Ajax.

Thanks!