GHC doesn't detect trivial complete pattern with the combination of ExistentialQuantification and ViewPatterns

This program exhibits the behaviour:

{-# LANGUAGE ViewPatterns, ExistentialQuantification #-}
{-# OPTIONS_GHC -fwarn-incomplete-patterns #-}

data Moo = Moo (Char -> Int)
spqr (Moo _) = undefined      -- Exhaustive pattern
foo (id -> Moo _) = undefined -- Exhaustive pattern


data Exists = forall a. Exists (a -> Int)
bar (Exists _) = undefined       -- Exhaustive pattern
baz (id -> Exists _) = undefined -- "Warning: Pattern match(es) are non-exhaustive"

GHCs output is puzzling:

$ ghc -c Exhaustive.hs 

Exhaustive.hs:11:0:
    Warning: Pattern match(es) are non-exhaustive
             In the definition of `baz': Patterns not matched: _

It can detect exhaustivity if you use either existentials OR view patterns by themselves, but not with the combination of the two together. Weird!

Trac metadata

Trac field	Value
Version	6.12.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture