in the one-page mode, Kanso takes several pages and compiles one long “one-page” view from them. For that view, you do need a separate page (this is the WordPress internal logic, similar to the fact that one needs a separate page for “hosting” the blog posts outside of the front page). Please try editing the pages directly, i.e. go to the “Pages” admin menu and find the pages which correspond to your “Writing”, “Photography”, and other titles.
this is not supposed to happen, and hasn’t been reported before; I will therefore need to ask for your website’s admin login and password to troubleshoot. You can send the information to firstname.lastname@example.org, no disclosure guaranteed.