Are new skinny leaves normal in flowering?

Yep, quite normal for some strains, especially when flowering commences, so nothing to be concerned over, nor is it a defect of any sort. Sometimes plants will have very broad indica leaves during veg, then when flowering is underway, start growing thin sativa like leaves. Not sure why, maybe having thinner/narrower leaves during flowering is an advantage to make it as easy as possible for male pollen to land on the pistils, which theoretically would be harder for plants with very wide leaflets. Purely a guess though. Hope this helps,.... Organoman.