AvailTC Invariant being violated

The AvailTC Invariant (from basicTypes/Avail.hs) states that:

If the type or class is itself
to be in scope, it must be
*first* in this list.  Thus,
typically: @AvailTC Eq [Eq, ==, \/=]@

Here is a case where this invariant is not upheld:

• pkgA/pkgA.cabal:

name: pkgA
version: 1.0.0
build-type: Simple
cabal-version: >= 1.2

library
  exposed-modules: A
  build-depends: base

• pkgA/A.hs

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeFamilies #-}
module A
  ( C(..)
  , T(TI)
  , error
  ) where

class C a where
  data T a

instance C Int where
  data T Int = TI { ti :: Int }

• pkgB/pkgB.cabal

name: pkgB
version: 1.0.0
build-type: Simple
cabal-version: >= 1.2

library
  exposed-modules: B
  build-depends: base, pkgA

• pkgB/B.hs

module B
  ( module A
  ) where

import A hiding (error)

Now, check out the exports for A vs. B:

$ cabal new-build pkgA pkgB --ghc-options -ddump-rn-trace | grep rnExports
Warning: The package list for 'hackage.haskell.org' is 38 days old.
Run 'cabal update' to get the latest list of available packages.
rnExports: Exports: [error, C{C, T;}, T{T, TI;}]
rnExports: Exports: [C{C, T;}, T{TI;}]

Why is T{TI;} in the second line not T{T, TI;}? Shouldn't the exports for B be identical to those for A (except for error)?

This is causing a crash in Haddock: https://github.com/haskell/haddock/issues/979.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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