rpmdb/rpmdb.c (rpmdbNextIterator):
  2418	    /* If next header is identical, return it now. */
  2419	/*@-compdef -refcounttrans -retalias -retexpose -usereleased @*/
  2420	    if (mi->mi_prevoffset && mi->mi_offset == mi->mi_prevoffset)
  2421		return mi->mi_h;
  2422	/*@=compdef =refcounttrans =retalias =retexpose =usereleased @*/

It looks like the condition never holds, because: 1) when doing mi_set,
each set element should be different; 2) when doing DB_NEXT, each header
instance should be different as well.