It happens in photoshop too, but you can change your layers to ‘smart objects’ which will make it so that the quality never deteriorates!
Oh wow, you’re right! And this deteriorated even worse than SAI’s did (5 passes vs. 14)! At least there’s no dark line. :U
Mmm smart layers. Such a great feature (in theory, since I’ve only used it once while testing/experimenting). If only I liked PS as much as I hate it.