How exactly should magazine unlock work?

Does the image on the lock screen should change every time i lock/unlock the phone? Because for me it changes like every two-three hours regardless of how many times i lock/unlock the phone.

Secondly, its weird but if I set one of my images as a home screen wallpaper, I get various images from Added By Me category of the magazine unlock as a lock screen wallpaper. But if I set one of the stock magazine unlock images as a home screen wallpaper, I get various magazine unlock images as a lock screen wallpaper.

Is it the same for everyone?