Skritter Not Properly Allowing me to Study Kana

I’m very confused. I’m using my android smart phone to study Japanese, but the Kana feature just doesn’t work properly. I have the “Study Kana” feature enabled, but sometimes Skritter still feeds me words with the Kana already filled in, and sometimes it allows me to practice writing them properly. I can’t find any rhyme or reason to this. Has anyone encountered a similar problem? How do I fix this?