Typed Template Haskell suppresses -Wunused-top-binds warnings

In this program:

{-# LANGUAGE TemplateHaskell #-}
{-# OPTIONS_GHC -Wunused-top-binds #-}
module Bug (a) where

a :: Int
a = $([| 42 |])
-- a = $$([|| 42 ||])

z :: Int
z = 42

GHC correctly informs me that z is defined but not used:

$ /opt/ghc/8.10.3/bin/ghc Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o, Bug.dyn_o )

Bug.hs:10:1: warning: [-Wunused-top-binds]
    Defined but not used: ‘z’
   |
10 | z = 42
   | ^

If I comment out the definition of a and replace it with a = $$([|| 42 ||]), however, then GHC doesn't report any warnings at all!

$ /opt/ghc/8.10.3/bin/ghc Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o, Bug.dyn_o )

I'm unclear why the use of typed Template Haskell would change things here, as I would expect -Wunused-top-binds warnings in both scenarios.