Problems disambiguating a record update with pattern synonyms

The parent of a pattern synonym record field is the pattern synonym itself, which I think makes sense (a pattern synonym behaves much like a data constructor). However, it seems that the following variant on #21443 causes GHC to trip over:

{-# LANGUAGE DuplicateRecordFields, PatternSynonyms #-}

pattern P :: Int -> Int -> (Int, Int)
pattern P { proj_x, proj_y } = (proj_x, proj_y)

pattern Q1 :: Int -> Int
pattern Q1 { proj_x } = proj_x

pattern Q2 :: Int -> Int
pattern Q2 { proj_y } = proj_y

blah :: (Int, Int) -> (Int, Int)
blah p = p { proj_x = 0, proj_y = 1 }

error:
    * GHC internal error: `T21443b.$sel:proj_x:P' is not in scope during type checking, but it passed the renamer
      tcl_env of environment: [auv :-> Identifier[p::(Int,
                                                      Int), NotLetBound],
                               rgF :-> Identifier[blah::(Int, Int)
                                                        -> (Int, Int), TopLevelLet {} True]]
    * In the expression: p {proj_x = 0, proj_y = 1}
      In an equation for `blah': blah p = p {proj_x = 0, proj_y = 1}
   |
   | blah p = p { proj_x = 0, proj_y = 1 }
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^