If this is true, it is annoying. I don't see why I have to automatically purchase them when my religion is already flourishing and not in need of help. All those science buildings that I'm planning on faith-buying really add up and I NEED faith for them.
Seems more like a bug than a mechanic, especially since I clicked an option to not have them auto-purchased.
It seems like a way of limiting the ability to hoard Faith until Industrial and then mass buying GS and GE. Whether you agree with this design decision or not (personally I like the way you can't stockpile faith in the early/mid game as you have to make pressing and difficult choices on what to spend it on) it is working as intended.