Originally Posted by Salathe

There's a very simple solution.

Change: (in the class2 constructor)
To:
Why does this work? It's all about the way that PHP4 handles passing around references to objects. The &$class1 argument for the constructor ensured that the argument was brought in by reference, but when it was being assigned to the class1 property the assignment was by value -- a copy of the object was made and assigned to the property.

When we changed the data property, it was only changing it in the copy and not the original. Using =& the variable is assigned by reference as we intended. Hopefully you can see now why this behaviour was changed in PHP5 to assign by reference by default. :)