TH vs. default function implementation: internal error

Testcase:

{-# LANGUAGE TemplateHaskell #-}
import Language.Haskell.TH
class Numeric a where
    fromIntegerNum :: a
    fromIntegerNum = undefined

ast :: Q [Dec]
ast = [d|
    instance Numeric Int
    |]

It gives an internal error:

InstanceGenerator.hs:9:13:
    GHC internal error: `Main.$dmfromIntegerNum' is not in scope during type checking, but it passed the renamer
    tcg_type_env of environment: [(rgd, Class `Numeric'),
                                  (rgf, Identifier `fromIntegerNum'),
                                  (rgm, Data constructor `Main.D:Numeric'),
                                  (rgn, Type constructor `Main.T:Numeric'),
                                  (rgr, Type constructor `Main.NTCo:T:Numeric'),
                                  (rgs, Identifier `Main.D:Numeric')]
    In the instance declaration for `Numeric Int'
    In the Template Haskell quotation
      [d| 
          instance Numeric Int where |]
    In the expression:
        [d| 
            instance Numeric Int where |]
Failed, modules loaded: none.

May be related to Ticket #4056 (closed) (?)

Trac metadata

Trac field	Value
Version	6.12.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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