[racket] TR: scope of universally quantified type variables is ... very strange?

I wrote a piece of code like this without thinking:

#lang typed/racket

(: f (All (T) (Number -> T -> T)))
(define ((f x) y)
  (ann y T))

... and then, after a second, was sort of flabbergasted that it worked.  What's the scope of the type variable T? Apparently I can use it anywhere in the definition of the identifier that it names? That seems really fragile. Am I misunderstanding this?

John

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