Pattern matching on OverloadedLists is erratic

Consider

λ> :set -XOverloadedLists 
λ> :t \[True] -> 'a'
\[True] -> 'a' :: (GHC.Exts.IsList l, GHC.Exts.Item l ~ Bool) => l -> Char
λ> :t \[not] -> 'a'
\[not] -> 'a' :: GHC.Exts.IsList l => l -> Char

The first type is expected, but the second one should include GHC.Exts.Item l ~ Bool -> Bool and Eq (Bool -> Bool). Currently e.g. (\[not] -> True) [id] evaluates to True.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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