[plt-scheme] behaviour of void?

Code:

(define x 2)
(void? (set! x 3))

In Advanced Student: produces `false'.
In Module (with addition of #lang scheme): produces #t.

Why?

Thanks.

(Not my question. I don't cover `void?', because I don't see much point 
to it, and I skip over Advanced Student to get to Module. Asked by 
people teaching the non-major course.) --PR