ApplicativeDo bug in ghc-8.2.1

appdo.hs

{-# LANGUAGE ApplicativeDo #-}

import Options.Applicative

main :: IO ()
main = undefined 
  
data Example = Example 
  { someBool :: Bool }

exampleP :: Parser Example
exampleP = do
  (a, b) <- toPair <$> boolP
  pure $ Example a
 where
  toPair :: Bool -> (Bool, Bool)
  toPair x = (x,x)

boolP :: Parser Bool
boolP = undefined