Sometimes the app needs to "scale down" a photo for you to be able to edit it due to hardware limitations of the phone. We found that editing was too slow at very high resolutions. If you have a more recent phone, the max size allowed will be larger than on a rather old one.
This does not ever scale down the original photo that you backed up to Picturelife though. Even if you save and replace, your original can still be accessed in future if necessary.
We suggest, for your own ease, that when you are editing on your iOS device and scaling down is necessary, you simply Create New rather than Replace.