This was added only after @jacksona ran into this problem. Since the stack does some complicated output buffering I figured it would be better to just warn against making things more complex than needbe.
I think it kind of reflects negatively upon stacks and makes users think that partials break some things. I think that is untrue – or at least I’m trying very hard to make it untrue 
-- and if there are bugs that are causing some things to break in partials I think they’re getting to be pretty tough to find.