Has anyone else noticed that when you go to strengthen a particular skill, it doesn't always give you the strength you've earned? It's really kind of maddening to me, because I've been trying to strengthen all my Spanish skills to the fullest extent, and it only sporadically gives me what I've earned. I know it has nothing to do how many hearts I have at the end, because on several occasions I've finished with three hearts and my strength is that area still doesn't improve.
Duolingo is awesome by the way, I really don't mean to complain! But I am curious as to what might be happening.