PHP - 将元素附加到数组的段错误

I have an array containing about 75 elements (not very deeply nested). When I try to add a new element with:

$myArray['mykey'][] = $newElement;

I get a segfault with php error 4. Is there a way to prevent from it? how can I change this code to avoid such things. Tried array_merge, array_unshift or += operation - all with the same result

Edit:

Sorry, here are details: PHP 5.5.9-1ubuntu4.14, Ubuntu 14.04 x64. Application also usess RabbitMQ, Redis, Elasticsearch

    public function modify($stock, $new) {

    if (!isset($stock['data_sets'])) {
        $stock['data_sets'] = []; 
    }

    $stock['data_sets'][]= $new;

    if (!isset($stock['garbage_sets'])) {
        $stock['garbage_sets'] = [];
    }

    return $stock;
}