PHP deprecated code with curly braces - no documentation about it?

Question

On a PHP 5.2 server this code was working, but it doesn't work any more under 5.6 :

$value = $record->{self::TABLE_METHOD}();

Under 5.6 I had to do that :

$abc=self::TABLE_METHOD;
$value = $record->{$abc}();

Otherwise said, it works using "self::TABLE_METHOD" via a variable, but not in curly braces.

Any help on why this is happening would be highly appreciated !

As requested, this is the "real" code :

class TActiveRecordGateway extends TComponent
{
    private $_manager;
    private $_tables=array(); //table cache
    private $_meta=array(); //meta data cache.
    private $_commandBuilders=array();
    private $_currentRecord;

    /**
     * Constant name for specifying optional table name in TActiveRecord.
     */
    const TABLE_CONST='TABLE';
    /**
     * Method name for returning optional table name in in TActiveRecord
     */
    const TABLE_METHOD='table';

    /**
     * Record gateway constructor.
     * @param TActiveRecordManager $manager
     */
    public function __construct(TActiveRecordManager $manager)
    {
            $this->_manager=$manager;
    }

    /**
     * @return TActiveRecordManager record manager.
     */
    protected function getManager()
    {
            return $this->_manager;
    }
    /**
     * Gets the table name from the 'TABLE' constant of the active record
     * class if defined, otherwise use the class name as table name.
     * @param TActiveRecord active record instance
     * @return string table name for the given record class.
     */
    protected function getRecordTableName(TActiveRecord $record)
    {

            $class = new ReflectionClass($record);

            if($class->hasConstant(self::TABLE_CONST))
            {
                    $value = $class->getConstant(self::TABLE_CONST);
                    if(empty($value))
                            throw new TActiveRecordException('ar_invalid_tablename_property',
                                    get_class($record),self::TABLE_CONST);
                    return $value;
            }
            elseif ($class->hasMethod(self::TABLE_METHOD))
            {
                    $value = $record->{self::TABLE_METHOD}();
                    # THE PROBLEM HAPPENS HERE : $value is empty