GHC sometimes ignores ' vs '' when quoting built-in names in TH

If I have

{-# LANGUAGE TemplateHaskell #-}

module Bug where

import Language.Haskell.TH

list = $( conE ''(:) `appE` litE (IntegerL 5) `appE` conE '[] )

this compiles, and evaluating list gives me [5].

But I would expect a failure, because no type exists named (:). (Important: I've used '' there, not ', which should work.)

I think that the problem is that isBuiltInOcc_maybe does not always check the namespace of the OccName it is looking up.