AllowAmbiguousTypes doesn't work with UndecidableSuperClasses

Given the code below, test1 and test2 are the same except the former has an ambiguous type and the latter does not. The compiler rejects the former and accepts the latter.

{-# LANGUAGE UndecidableSuperClasses #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE TypeFamilies #-}

class A (T a) => A a where
    type T a

test1 :: forall a. A a => ()
test1 = ()

test2 :: A a => proxy a -> ()
test2 _ = ()

Trac metadata

Trac field	Value
Version	8.0.1-rc3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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