OO-problem

Hi,

I'm experiencing the following problem when I try to implement an 
OO-model in PHP:
If a class, say A, has more than 1 method with equal names, say b, and 
different signatures and one of these methods b of an instance A is 
called, then PHP always delegates that call to the first method that 
appears in the code.
Example:

class A {
   function b () {
       ...
   }
   function b ($var) {
       ...
   }
}
$anInstance = new A;
$aReturnValue = $anInstance->b (...) // Won't work

Is this a bug or is there any other reason for this behaviour?

Thanks,
Bas