
The preparing your system for Stackage page[1] has those auto-updated
Michael Snoyman
You already identified the downside with this: you may magically be upgraded to a new version of a package. If you really want to do this, you can, but my recommendation is to manually decide to upgrade your Stackage snapshot consciously instead of letter an arbitrary Jenkins build server make the decision for you.
I'm using Stackage as a QA'd Hackage. It sounds like you see it more as a server-side cabal freeze.