Proposed resolution:

This wording is relative to N4659.

1. Edit [util.smartptr.shared.atomic] as indicated:

   template<class T>
     bool atomic_compare_exchange_weak_explicit(
       shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
       memory_order success, memory_order failure);
   template<class T>
     bool atomic_compare_exchange_strong_explicit(
       shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
       memory_order success, memory_order failure);
   

   […]

   -35- Remarks: Two shared_ptr objects are equivalent if they store the same pointer value and share ownership, or if they store the same pointer value and both are empty. The weak form may fail spuriously. See 32.6.1.