Panic while printing levity polymorphism error

Program

{-# LANGUAGE UnliftedNewtypes #-}                                               
{-# LANGUAGE ExplicitForAll #-}                                                 
{-# LANGUAGE PolyKinds #-}                                                      
                                                                                
import GHC.Exts                                                                 
                                                                                
newtype Id (a :: TYPE r) = Id a                                                 
                                                                                
foo :: forall r (a :: TYPE r). Id a -> Id a                                     
foo x = x

Output

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.9.0.20191008:
	isUnliftedType
  Id a_a1g7 :: TYPE r_a1g6
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1179:37 in ghc:Outputable
        pprPanic, called at compiler/types/Type.hs:2229:10 in ghc:Type

Expected output

    A levity-polymorphic type is not allowed here:
      Type: Id a
      Kind: TYPE r
    In the type of binder ‘x’

The issue seems to be specific to binders of types that are unlifted newtypes.

Environment

GHC HEAD