Source:

http://groups.google.com/group/recaptcha/browse_thread/thread/e870492de512a2ad

"We've pushed a change which fixes the problem with the audio CAPTCHA.
Thanks to everyone who brought it to our attention.

Best,
The reCAPTCHA team"

Good pick Juha-Matti,
yes it was a big fail from reCaptcha, i'm surprised that no attack with that has been uncovered yet.

Yes, it really is a surprise.