Maybe D is right about GC after all !

[Tony]

I have heard with regard to reference counting as is done in 
Python, that if two objects each have a reference to the other, 
that they will never be deleted, even if neither is used 
elsewhere in the program. Garbage collection is not supposed to 
have that issue, although I don't know how a garbage collector 
determines that there usage is just via each other and that they 
can be deleted.