Data.Vector.Mutable field can not be written/set properly? : Haskell

Question

I have struggled for days to compose a data structure that has a field of mutable value of Data.Vector.Mutable

I confirmed Data.Vector.Mutable itself behaves as I expected; however once it's included into a structure, somehow stops working against my expectation.

Below is a demo-code that simply has newVal, getVal and setVal targeting the mutable field value of the structure.

newIO is the constructor of the data structure typed as newIO :: a -> A a.

module Main where
import Control.Monad.Primitive (PrimMonad (PrimState))
import qualified Data.Vector.Mutable as M 
------------------------------------ 
data A a = A
  { ioVal :: IO (M.MVector (PrimState IO) a)
  }

newIO :: a -> A a
newIO = \a -> A (newVal a)
------------------------------
newVal :: a -> IO (M.MVector (PrimState IO) a)
newVal = \a -> do
  val <- M.new 1
  M.write val 0 a
  return val

getVal :: A a -> IO a
getVal = \aA -> do
  val <- ioVal aA
  M.read val 0

setVal :: a -> A a -> IO ()
setVal = \a -> \aA -> do
  val <- ioVal aA
  M.write val 0 a
------------------------------
main :: IO ()
main = do
  let ioA = newIO (5 :: Int)
  (getVal ioA) >>= print -- 5
  setVal 10 ioA
  (getVal ioA) >>= print -- 5 ?? expected 10

So, here, to confirm the basic behavior of set/get of the structure, I try to create, read, (re)write, and (re)read the mutable value of the field; however, it does not work as expected as the set should perform.

What's wrong with the code? Please advise.