Re: Using to sync gmail with S5
That's Google. If you allow Google backup to run, anytime you sign into a new device as the owner, or do a factory reset (which requires you to sign in as the owner) your Play Store account installs the apps from your installed list. This happened when I bought my M7, upgrading from the Rezound. Now if it would just save your sign-ins and game saves it would be perfect.
Added note for those who may find this thread later;
As for your account working on another device I never believed it to be the account. And even though both devices have a GMail app, in this case, the app will not be the same necessarily from one device to another. Apps usually have to be tweaked a little from say tablets to phones, and from 4.4" screens with physical buttons to 5.1" screens with virtual buttons. The app is essentially the same but there are often minor differences, to say that it could still be the app even though it is working on one device and not on another because they are different versions of the same core app.
I realize that you've solved your issue, some apps have "refresh rates" or "sync intervals". I think the Facebook app is one that does and I believe my Maildroid app is another. So for those concerned about the amount of data they use these settings help them use less, because each request sent to check for new and each response, positive or negative, uses a small amount of data. By setting the refresh rate to a few less times each day one can reduce this load. Although I've still never heard of an app with a "days" refresh rate, seems excessive. Some apps will also have refresh over WiFi only options, like G+ Backup, which only transmits data when a WiFi connection is present. I don't know every app, in fact I know very little about most of the stock apps at all, because I've replaced them with other apps that offer me more or that I like better. So I was just guessing based on options I've found in other apps that your app may also have these options. In older versions of Android you could also set a refresh rate for some items in the Sync menu of the OS. I think that has died out though.