Hi Stefano,
the list is sortable but when you change the context (e.g. you go to the details page and you come back) the user defined sorting is not preserved. This is the current behavior of the component so if you want to obtain the explained feature, you can try to create a custom component based on the List that extends it and implements the preservation of the list (sort).
To create and debug a custom component you can refer to these articles of our knowledge base:
http://www.webratio.com/learn/learningobject/custom-unit-guide
http://www.webratio.com/learn/learningobject/how-to-debug-the-code-of-a-custom-unit-inside-the-web-application