Paintstorm doesn't open .jpeg. Not a huge problem because renaming them to .jpg allows Paintstorm Studio to open them. Still, kind of weird that they don't open even if they're valid image files.
Also images from Twitter don't open with an error message that says progressive images can't be opened. It would be nice if those could be opened too so you wouldn't have to save the file as a .png or something before opening it.