inconsistent behavior of caches_page method

ruby version : 1.8.6 rails version : 2.0.2 os : ubuntu 7.10

class StoreController < ApplicationController

    caches_page :index

    def index

        do something

    end

    def expire

        expire_page :controller=>'store', :action=>'index'

    end

end

when i visit: http://localhost:3000/store, a "RAILS_ROOT/public/
store.html" will appear

as i visit: http://localhost:3000/store/index, a "RAILS_ROOT/public/
store/index.html" will appear

the expire method in my class will delete the file "RAILS_ROOT/public/
store.html"

the problem is: {:controller=>'store',:action=>'index' }--->url_for
method----->'/store' ,so expire_page will delete the file
store.html.

if i don't use index action, it will not be a problem, but, anyone
have better idea? thanks for the reply.