Why is Google Play updating apps over data even when I have my settings set to Wifi only?

[AC Question]

I have noticed that many of the Google standard Apps (Newsstand, Play Music etc.) and some others (Amazon Prime Music for example) will update when I'm not connected to a Wifi network and I have made sure several times that I have my settings set to Wifi only. I don't want to have to switch to manual updates because it is convenient they update usually when I'm asleep.

Is anyone else having this issue? They update when I'm at work not connected to Wifi and when I have barely any data service, so it drains my battery too!