Strange behaviour when shadowing variables in Elm

shadowing.elm

import Graphics.Element (..)
import Text (..)

type alias A = { a: Float }

-- Why does this not work?
increment1 : A -> A
increment1 ({ a } as aye) =
  let a = a + 1
  in  { aye | a <- a }

-- .. but this does?
increment2 : A -> A
increment2 ({ a } as aye) =
  let newA = a + 1
  in  { aye | a <- newA }

main : Element
main =
  let aye = { a = 1.0 }
  in  plainText (toString (increment1 aye))