Now if you sort tasks by list they are sorted by list name. However, there's a feature in the app allowing you to manually sort which list (or tag) goes after which in the menu. Now it only has an effect on the menu itself. I think this manual sorting should influence the list sort and actually every interaction element where list of lists is displayed.
For example, I have lists One and Two. Then I manually move Two up, so that they appear as Two, One on the menu. Then I sort and/or group my tasks by list. I've got One, Two when I want Two, One.