caches_action not generating full parameter route

Hi there,
I have a URL like this:
/artworks/show/4
I've turned on caching in development mode, and my controller says:

  caches_action :index, :list, :show

as well as

  def show
    @artwork = @artist.artworks.find(params[:id], :include => :tags)
    @tags = @artwork.tags
  end

but for some reason i only ever get the cache file:
/artworks/show.cache
with no id parameter

I'm running 1.2.3
anyone have any ideas?

thanks
dorian

ok, I answered that myself.
I had a route that was biting before the one I was expecting.
note to self - check routes, regularly.