forkIO and not -threaded

Hi,

main = do
 forkIO $ print "yes"
 print "done"

Compiled without -threaded, on 6.2.2 gives

"yes"
"done"

on 6.4.2

"done"

Seems the semantics of forkIO in this case has changed completely?

Of course, I actually wanted -threaded and had forgot it, so I'm
entirely happy if it just raises an error :)

Thanks

Neil