Mutually recursive equality constraints

Given this piece of code:

{-# LANGUAGE TypeFamilies #-}

class C a where
  type T a :: *

f1 :: T a ~ () => a
f1 = f2

f2 :: T a ~ () => a
f2 = f1

GHC complains:

    Couldn't match expected type `T a ~ ()'
           against inferred type `T a1 ~ ()'
    When matching the contexts of the signatures for
      f1 :: forall a. (T a ~ ()) => a
      f2 :: forall a. (T a ~ ()) => a
    The signature contexts in a mutually recursive group should all be identical
    When generalising the type(s) for f1, f2

Is this a bug? Enabling RelaxedPolyRec fixes the problem. Should TypeFamilies—just like GADTs—imply RelaxedPolyRec?

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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