Wrong warning by -Wincomplete-patterns

Wrong warning occur where I use -Wincomplete-patterns with OverloadedLists and TypeFamilies.

{-# LANGUAGE OverloadedLists #-}
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}

class Foo f where
	type It f
	foo :: [It f] -> f

data List a = Empty | a :! List a deriving Show

instance Foo (List a) where
	type It (List a) = a
	foo [] = Empty
	foo (x : xs) = x :! foo xs

Pattern match(es) are non-exhaustive In an equation for `foo': Patterns not matched: []

Trac metadata

Trac field	Value
Version	8.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler
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