Anonymous users getting previous users data returned from ahah function

My form that uses ahah_helper will generally be submitted by anonymous users. My issue is that when caching is turned the ahah comes back with form data from a prior anonymous user's submission. The form loads properly so it is not that the storage isn't getting unset by the ahah_helper_real_submit function. Turning off the cache temporarily fixed the issue, but long term, the site needs caching for performance reasons.

I believe that the root cause is when the function ahah_helper_render is called, the form is retrieved from the cache using the form_build_id. At least for me, this form_build_id was the same for all anonymous users so fetching the form from cache grabs someone else's data. Maybe my drupal or implementation is causing it. I tried, unsuccessfully, to find a way to get a new form_build_id generated for anonymous users.

The work around I came to was to call cache_clear_all() at the end of my submit handler. I expect that this is not the best fix, but my form is only going to get used a few times a week so clearing the cache each time is not expensive for me.

I am not sure if clearing the cache is something that the ahah_helper_real_submit should do or if better done in the submit handler of the form.

The cache_clear_all function does allow you to target a specific things in the cache to clear so maybe that is a good compromise. Here is what seems to be a viable option I found in the drupal_process_form function. I will attempt to test at some point soon. I expect that this would make the cache clear expense negligible for most any implementation.

<?php
function ahah_helper_real_submit($form, &$form_state) {
  unset($form_state['storage']);

  cache_clear_all('form_' . $form_state['values']['form_build_id'], 'cache_form');
}
?>

Finally, in my troubleshooting, I noticed in the api that the form_get_cache function passes &$form_state as a reference, but ahah_helper argument has just $form_state. Not sure if this matters here..