It's called cracking. The sail will eventually start to get tiny pin holes where the cracking is occuring. They will all do this with enough use but on the trailing edge it is because it was left on the beach flapping against the sand as Bain stated. You'll notice the material is less crisp where this is occuring, and feels more cloth like.
Yes this is exactly how it fells..Its fells alot softer like cloth than any other spot of the kite..So is anything i can do about it ?Or i just ride and care of it abit more?...I am abit worried i can say and confused..