Closures are availble automatically on parrellel workers, but normal functions are not

On Julia 0.5, I encountered the following strange behavior.

addprocs(4)
function adder_gen(n)
    function add(x)
        x+n
    end
end
f_closure=adder_gen(5)
fetch(@spawn f_closure(5))

Normally, I would expect the last line not to work. There was no @everywhere preceding the closure generation. If the this was done with a normal function, an error would be generated.
I believe an explanation is in order. There is nothing in the manual that would suggest this behavior.