Fairly normal for cannabis to have the odd shaped leaf every now and then and it is not something to worry about. No plant will have 100% perfect leaves, 100% of the time. In my long experience I have seen all sorts of weird shapes in the leaves and unless every leaf is weird, there really isn't any need for concern. It is just a strange genetic mix up that has caused it, not a deficiency, too much sun, high temps or anything else. It is a bit like getting a single strand of blond hair growing on a red headed person. There is nothing wrong with the person, just a weird hair.
Hope this helps,..............
Organoman.