Have you tried turning off notifications for the Google Play store too?
I have that one off as well. Pretty much all my notifications are off except gmail and hangouts. But I'm not having a problem, and while it's being reported frequently, it's also not widespread.
I've been doubting other reporters having both settings (in game and app settings) set to off, but I trust you as a competent (ex)mod should be able to handle that. Only other thing I could suggest is the old stand by, uninstall/reinstall? Then of course switch them back off and see if they take effect.
Really weird...
