What's goin on with my skolems

skolem.hs

-- This reproduction can be played with using `ghcid --allow-eval`

{-# language RankNTypes #-}

import Control.Monad.ST

newtype IdT m a = IdT { unIdT :: m a }

-- $> :set -XRankNTypes
--
-- @jkachmar pointed this out to me, and I'm at a loss. If we pattern match
-- directly on the `IdT` transformer, then the result value results in the
-- @s@ type variable escaping somehow.
--
-- $> :t (\(IdT x) ->  runST x) :: (forall s. IdT (ST s) a) -> a
--
-- <interactive>:1:21: error:
--     • Couldn't match type ‘s’ with ‘s0’
--       ‘s’ is a rigid type variable bound by
--         a type expected by the context:
--           forall s. ST s a1
--         at <interactive>:1:15-21
--       Expected type: ST s a1
--         Actual type: ST s0 a1
--     • In the first argument of ‘runST’, namely ‘x’
--       In the expression: runST x
--       In the expression:
--           (\ (IdT x) -> runST x) :: (forall s. IdT (ST s) a) -> a
--     • Relevant bindings include
--         x :: ST s0 a1 (bound at <interactive>:1:8)
--
--
-- But this one works just fine, using the runner function.
--
-- $> :t (\a -> runST (unIdT a)) :: (forall s. IdT (ST s) a) -> a
--
-- What gives?