The ~/.stack/global/stack.yaml file seems to be a common source of confusion (see #964, and I've seen the same thing a few other times). The stack.yaml documentation is pretty clear about its use, but I suspect in many cases people are just seeing a stack.yaml that exists under their ~/.stack and assuming it sets global default options without ever looking at that part of the documentation.

I'm thinking we should have stack put a comment at the top of ~/.stack/global/stack.yaml when it is generated stating what its use is and pointing people to the right place to put global defaults.