Desired behavior: you're working on a project that uses LTS 2.9. You leave that project and go to a directory which has no stack.yaml file. You run stack runghc foo.hs. Instead of using some random snapshot, it should use the most recently used snapshot (LTS 2.9) so that there's a good chance that your desired libraries are available. It should also print out a message to the user explaining what happened and recommending a config file for more determinism.