list_fields not working on query

[eluser]cogito[/eluser]
I do not have any particular code, I have just tried to create a general code to get query result and display it as a html table. I have tried to get query from model and call

Code:

$query->list_fields()

to get fields (get user friendly column names etc.).
But the function doesn't return anything. It works when I call

Code:

$this->db->list_fields('users');

I'm doing it currently, but it gives two queries to database.
Should I do anything more to enable list_fields() for a query returned by

Code:

$query = $this->db->get('users');

?
I have used most simple calls, examples from user guide (user guide).
I'm using simple MySQL database, currently connecting to it as a root (I will change it later on to use more restricted account).