Try static instance inside class :
New class Singleton1 created 
Using old class Singleton1

Notice: Only variables should be assigned by reference in %sbug32322.php on line 49
Using old class Singleton1
Try static instance inside function :
New class Singleton2 created 
Using old class Singleton2

Notice: Only variables should be assigned by reference in %sbug32322.php on line 55
Using old class Singleton2
Class Singleton1 destroyed at script end
Class Singleton2 destroyed at script end