i'v tried this out: i've taken several pictures with scannable with different things, a folder, advertising, a letter, an other write book i use. in the same process, i took a picture of my moleskine, the page is blank. all other files are ok.
my app is in german so the settings are: no flash, capture is automatic.
what i figured out, is, when i took the picture manually without a frame around the book, it doesn't work. if i took the next picture in the same session without a frame around, this works. next picture with a frame or lets say space around, so i can see the desktop, it doesn't work.