Leveled up dark arts by picking up a Sandal Wood.. ..
As the title says.. I tapped a sandal wood, and the prompt that I leveled up Dark Arts popped up.. and according to my skill screen, it did level up for real. And I have not battled for about 10 minutes when it happened..
Now it leveled up from making a potion..
@henric-melin if you level up more skills at the same time the popup system becomes a bit slow