Bogus postmaster-only contexts laying about in backends

I happened to notice these in a backend's memory context dump:
 ident parser context: 0 total in 0 blocks; 0 free (0 chunks); 0 used hba parser context: 7168 total in 3 blocks; 3920
free(1 chunks); 3248 used
 

Is there a good reason why these weren't made children of the
PostmasterContext, so that they'd go away inside backends?
        regards, tom lane