Attempt at levity polymorphic pattern synonym causes panic

If I say

{-# LANGUAGE StandaloneKindSignatures, MagicHash, ExplicitForAll, PolyKinds,
             DataKinds, UnliftedDatatypes, PatternSynonyms #-}

module PatSyns3 where

import GHC.Exts

type LPInt :: forall (l :: Levity) -> TYPE (BoxedRep l)
data LPInt l = MkI Int#

pattern MkIPS :: Int# -> LPInt lev
pattern MkIPS n = MkI n

GHC says

<no location info>: error:
    panic! (the 'impossible' happened)
  GHC version 9.3.20210916:
        tyConAppTyCon
  lev_a2ju
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc:GHC.Utils.Panic
        pprPanic, called at compiler/GHC/Core/Type.hs:1431:52 in ghc:GHC.Core.Type

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

I expected the original program to be rejected, as it seems to be attempting to write a levity-polymorphic pattern synonym. But it shouldn't cause a panic!