This is a very quick fix for people having a very long list of categories inside prestashop.
The problem occurs because in the product edit page from admin you need to scroll a lot to get to the save button each time.

Enough with the talking, here is the piece of code:
open admin/tabs/AdminProducts.php
replace:

                        '.$this->l('Catalog:').'
                        
                            

with:

                         '.$this->l('Catalog:').'