The results are saved automatically, but if they were not, a prompt should appear when you close the exercise asking you whether you would like to save the results or not. This message is however not displayed if only a few questions have been answered.
Well ... sometimes my statistics don't get recorded. Like yesterday I was doing a custom exercise that is showing SLOW improvement and I wanted to look at my score over the last few days. I went to look at the results and that session just wasn't there.
I can't predict when my statistics do and don't get recorded. Usually I don't have a reason to look at them, but when I do it's ... statistical ... whether they show up in the record or not.