See Core issue 476.

Discussed in Rapperswil 2014. EWG thinks there's no design defect here, and suggests that a placement array new should not have such implementation-defined overhead. EWG suggests that CWG should clarify that placement array new T[n] needs n*sizeof(T) bytes of memory, and clarify that an operator delete must only be called if the corresponding operator new has been called. Ask James Dennett/Chandler Carruth for any more feedback.