Proposed resolution:

This wording is relative to N3691.

1. Change [optional.object.assign] as indicated:

   optional<T>& operator=(const optional<T>& rhs);
   

   […]

   -8- Exception safety: If any exception is thrown, the values of init and rhs.init remain unchanged. If an exception is thrown during the call to T's copy constructor, no effect. If an exception is thrown during the call to T's copy assignment, the state of its contained value is as defined by the exception safety guarantee of T's copy constructorassignment.