It seems there is a bug with leveling up.
In the frame of the story i performed a couple of tasks which increased my Agility to 12 and after doing the frog hunt quest I have reached level 2. With it my Agility got reducd to 10 (so basically the previous amount before the story events which increase it).
Edit: sorry, I'm playing the free 2.1 version. Don't know whether the bug exists in the 2.5 version.