Why are LSP violations in PHP sometimes fatal, and sometimes warnings?

This LSP violation raises a Fatal Error:

abstract class AbstractService { }
abstract class AbstractFactory { abstract function make(AbstractService $s); }
class ConcreteService extends AbstractService { }
class ConcreteFactory extends AbstractFactory { function make(ConcreteService $s) {} }

This LSP violation also raises a Fatal Error:

interface AbstractService { }
interface AbstractFactory { function make(AbstractService $s); }
class ConcreteService implements AbstractService { }
class ConcreteFactory implements AbstractFactory { function make(ConcreteService $s) {} }

While this LSP violation only raises a Warning:

class Service { }
class Factory { function make(Service $s) {} }
class MyService extends Service { }
class MyFactory extends Factory { function make(MyService $s) {} }

Why? Shouldn't they all be fatal since they're all contravariant?