Guestbook and Cache

I have cache turned on with no 'minimum cache lifetime'.
When I tested a guestbook for my site, I wrote an entry and it didn’t appear immediately. But ordinary nodes comments appears instantly. I guess if my visitors would write an entry, because of this, they would try to write a new one and after a while they would realise that they wrote two. I very like to add a guestbook to my site, but because of this I can't. I think this is a feature request. Or maybe I am doing something wrong? Thanks.