I think i found an syntax error in eZPersistentObject

https://github.com/ezsystems/ezpublish-legacy/blob/master/kernel/classes/ezpersistentobject.php#L1342

this code
if ( isset( $def["functions"][$attr] ) )
{
return $this->$def["functions"][$attr]();
}
should be

if ( isset( $def["functions"][$attr] ) )
{
return $def["functions"][$attr]();
}

I don't know if this code is used in any case.
But i think this code could not work.