This is a very strange thing that I only noticed yesterday.

I was backtraining in the crystal forest, and I noticed that while I was consistently able to hit the baby gryphons with my light and heavy thrown weapons (103 and 56 ranks respectively) with lob, I was not gaining experience in either of those two skills. I had previously been training polearms (164 ranks) and bows (124 ranks) without any problems. If I lobbed those weapons at the fledgeling gryphons, I would start to learn like normal. I have never had this problem with any other creature as I was using the same weapons I had always used to train these skills. I also have no idea if this is something that is specific only to the gryphons in this location.