PatternSynonyms confuse exhaustiveness check

I just noticed some odd behaviour when (ab)using pattern synonyms in the following code (whose style I don't really endorse):

{-# LANGUAGE PatternSynonyms, LambdaCase #-}

module PatSyn1 where

import System.Directory (doesFileExist)

pattern Found    = True
pattern NotFound = False

readConfigFile :: FilePath -> IO ()
readConfigFile filePath = doesFileExist filePath >>= \case
    Found    -> putStrLn =<< readFile filePath
    NotFound -> putStrLn "File does not exist."


pattern Void = ()

foo :: () -> ()
foo Void = ()

Results in

/home/hvr/Haskell/PatSyn1.hs:(11,54)-(13,47): Warning:
    Pattern match(es) are non-exhaustive
    In a case alternative: Patterns not matched: _

/home/hvr/Haskell/PatSyn1.hs:19:1-13: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for ‘foo’: Patterns not matched: _

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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