Problem with the Comments

Hello,

i have a problem with the comments in my website.
If a reply to some user, my comment appears in the bottom of the comment part and not directly after the comment
(non lo so scrivere in inglese: i commenti non sono più nidificati, appaiono uno dopo l’altro…)
how can i solve this problem?
Thank you for attention

Elvio Rocchi

The page I need help with: [log in to see the link]