special variables $tag and ${0} are empty

contents of 'startup':

set autolog on
set autolog_path ~/Documents/irclogs/$tag/${0}/${0}-%Y-%m-%d

but there will be only one log file created, named
  ~/Documents/irclogs/-2013-05-26


in 'config' in 'settings' I also have:
  "fe-common/core" = {
    autolog = "yes";
    autolog_path = "~/Documents/irclogs/$tag/${0}/${0}-%Y-%m-%d";
  };