In PHP 5.3, when accessing a string as an array, if the key was a string (non-existing because, for strings, the keys are integers), first char was returned. Probably it converts the string to integer, therefore to 0.
PHP 5.4 throws a warning.
$article; // this holds '98765' but you expect an array
// You try to read a value from your "array"
// PHP 5.3 : nothing
// PHP 5.4 : Warning: Illegal string offset at line ...
$value = $article['id_article'];
var_dump($value); // returns: string(1) "9"
.