Kind signature not accepted (singletons)

I don't understand the rules for kind signatures / CUSKs but this works

import Data.Singletons.Prelude

data Some (f :: u ~> v) where
  Some :: Sing (x :: u) -> f @@ x -> Some f

but this doesn't?

import Data.Kind
import Data.Singletons.Prelude

data Some :: (u ~> v) -> Type where
  Some :: Sing (x :: u) -> f @@ x -> Some f

--        • Expected kind ‘u ~> v’, but ‘f’ has kind ‘u ~> *’
--        • In the first argument of ‘Some’, namely ‘f’
--          In the type ‘Some f’
--          In the definition of data constructor ‘Some’
--      |
--    5 |   Some :: Sing (x :: u) -> f @@ x -> Some f
--      |                                           ^
--    Failed, modules loaded: none.

I have to quantify over them for it to work forall u v. (u ~> v) -> Type, if this is expected I feel like the error message ought to be improved.

Trac metadata

Trac field	Value
Version	8.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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