Consider this

{-# LANGUAGE PatternSynonyms, ExistentialQuantification #-}
module ExQuant where

data Showable = forall a . Show a => Showable { fs :: a }

pattern Nasty{fn} = Showable fn

qux1 = fs (Showable True)
qux2 = fn (Showable True)

I have discovered that in qux2, the use of fn is a HsVar, not a HsRecFld as it should be. And the occurrence of fs in qux1 is indeed a HsFld.

I'm not sure of the consequences, but it looks inconsistent and wrong.