[racket-dev] for/first and multiple values

Why is the body of a for/first a single valued context?  I would expect 
this to work:

   (let ((s (set 1 3 10)))
     (for/first ((x (in-set s)))
       (values x (set-remove s x))))

But I get:

    context expected 1 value, received 2 values: 1 (set 3 10)

(By the way, this operation would be nice to have in racket/set.)

David