PS Express on iOS exploding photos

Over the past few weeks I've noticed that PS Express (iOS) is exploding the size of my photos. No matter how I save an image, the new one is SO MUCH BIGGER. I just did an experiment where I opened a 1200x1200 pixel photo. The iOS Photos app lists it as: 1MP, 1200x1200, 589 KB. I opened it in PS Express on my phone, desaturated the photo without making any other changes, and saved it (I have "Save as copy" enabled, btw, so it creates a new file). The new gray-scale photo has the following info in the iOS Photos app: 13MP, 3600x3600, 2.1 MB. Why is this happening? I can find nowhere in the setting to make this insanity stop.