@Anonymous I know it's been a long time (almost 4 years!!) since you had asked this question. I also had the same question before I stumbled upon this page.
I found out the answer after some quick testing and thought other folks may find it useful
Whenever you have a "Distinct" keyword in the mapping load, Qlik for some reason shows only "1 lines fetched" in the logs. But, it still generates the entire mapping load.