In the documentation (http://www.php.net/manual/en/language.oop.constructor.php) you defined the following rule:

"If a class has no constructor, the constructor of the base class is being called, if it exists"

This worked in PHP 4.0.6 for me. After upgrading to Version 4.1.1, it doesn't.

Here are my test-scripts. The first one ends up with no output or the errormessage: "Fatal error: Cannot instantiate non-existent class: mountainbike in
/www/testOO.php on line 15". 

actually, the behaviour seems to be undefined. 

The second one works, as it should be, but only because of actively calling the constructor of the base class. 

FIRST:
<?php
class Bike {
  function Bike() {
    echo 'Constructor of class "Bike"';
  }
}


class MountainBike extends Bike {
}

$mb = new MountainBike();
?>

SECOND:
<?php
class Bike {
  function Bike() {
    echo 'Constructor of class "Bike"';
  }
}


class MountainBike extends Bike {
  function MountainBike() {
    parent::Bike();
  }
}

$mb = new MountainBike();
?>

Greetings, 
Arash

My configure line is:
./configure \
--with-apxs=/usr/local/apache/1.3.20/bin/apxs \
--enable-track-vars \
--enable-ftp \
--with-zlib \
--with-gd \
--with-pdflib \
--with-sockets \
--enable-sockets \
--with-sysvshm \
--with-sysvsem \
--enable-dbg=shared \
--with-dbg-profiler \
--with-mysql=/usr/local/mysql/current \
--with-pgsql=/usr/local/pgsql \
--with-mcrypt