Re: memory leak detection techniques

In my non-MFC DLL I have a global instance of an object of the form

CMyCollection : public std::vector<CMyThing>;

Its normal constructor is called on startup, which just creates and empty
collection.
It is only called once.
It is filled in (also once) with a method of CMyColllection schematically of
the form

CMyCollection::FillIn()
{

   CMyThing thing;

   for( allthings )
   {
       thing = .... // fill in the thing
       push_back( thing ); //*********
   }
}

It is usually not changed, and lasts until the program shuts down.
It is never copied. (It has a copy constructor, because I feel nervous
without them, but it is never called.)
The destructor is called once, and just calls clear() (because I feel it
is neat to do so).

I am being told that the memory leak is associated with the CMyThing's copy
constructor invoked by push_back() above.

How can that be?

Even stranger, I have had all of this present in the code for years and a
memory leak has only been reported recently.

Any ideas gratefully received.