ghc doesn't agree with its own inferred pattern type

GHCi, version 8.1.20160419:

pattern F a <- (($ 'a') -> a)

>>> :i F
pattern F :: b -> Char -> b 	-- Defined at /tmp/tTaa.hs:24:1

Putting them together:

-- tTaa.hs:25:9: error: …
--     • Pattern synonym ‘F’ has one argument
--         but its type signature has two
--     • In the declaration for pattern synonym ‘F’
Compilation failed.
pattern F :: b -> Char -> b 
pattern F a <- (($ 'a') -> a)

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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