How list works

1. runs the query, gets the reultset
2. looks at all the columns (query items) and check the usage attribute
3. it will distinguish between facts and everything else: attributes and identifiers
4. makes sure that there is only one row for each unique combination of attributes and identifiers
5. when multiple rows are found these are groupped by aggregating all the facts

This means you have to be extra careful to make sure that the usage attribute is set properly.
Usually it is... but there's no guarantee.
If you see too many rows or values being summed up then keep this in mind.