"Pattern match has inaccessible right hand side" with TypeRep

When I say

{-# LANGUAGE PatternSynonyms, ViewPatterns #-}

module Bug where

import Type.Reflection

pattern X arg <- (checkFun -> arg)

checkFun :: TypeRep fun -> a
checkFun = undefined

f x = case (x, True) of
          (X _, _) -> 5
          _        -> 6

g x = case x of
          (X _) -> 5
          _     -> 6

I get

Bug.hs:13:11: warning: [-Woverlapping-patterns]
    Pattern match has inaccessible right hand side
    In a case alternative: (X _, _) -> ...
   |
13 |           (X _, _) -> 5
   |           ^^^^^^^^^^^^^

I'm troubled by two things:

1. There's nothing inaccessible about my right-hand side.
2. This happens only for f, not g. If there's no tuple, there's no problem.

Note that this problems requires TypeRep. Even another polykinded tycon (like Proxy) didn't trigger the problem.

Trac metadata

Trac field	Value
Version	8.5
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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