Rails - Jun 2006 - Action caching with params

I was attempting to cache an action that had a URL like this:

http://foo.com/controller/action?years[]=2005&years[]=2006&bar=5&baz=blue

which returns different data than, say

http://foo.com/controller/action?years[]=2004&years[]=2005&bar=6&baz=red

However, the cached fragment would always be named
foo.com:3000/controller/action.cache, no matter what parameters where
passed in, which would result in incorrect data being rendered on a
cached page.

I eventually tracked the culprit to ActionController::Base#url_for,
which the fragment cacher calls well reading and writing the fragment.
 In my controller, I added this:

def url_for(options = nil, *parameters_for_method_reference)
   super( options ? options : params, parameters_for_method_reference)
end

which sends the params hash as options, if no options are specified
(as is the case with the cacher).

So is this a bug in rails or a misunderstanding on my part as to the
proper behavior?  Am I doing something dangerous here by fiddling with
one of the more used methods?

Thanks,
Andrew