If added new form element, and then reload the ahah form page, add new form element again, it will save elements last time added

It's a cache problem, if disabled the cache mode in performence setting, it will be solved. I think disable cache mode will decrease performence of website. So I use this code:

cache_clear_all();

It will delete all pages cache, if just delete ahah form page cache is better, the code is:

cache_clear_all('page_link', 'cache_page', true);

But this code doesn't work, i don't know, somebody can tell men?