As per my posts: http://www.flyertalk.com/forum/14139045-post47.html

Available only from 24-30June, and 01-30Sep from GRU only, based on outbound. Fare is valid for 2 months, but no changes to dates.

QR has blocked off all BCN availability in W class, but MAD still available.
W class is also extremely limited from GRU. I think in Sep only a few dates are left. Next up is "V" class. Also limited.

No other fare exists. If searching beyond Sep 30th. No fare.

As of date, the YQ is not charged. It is clearly an error. As EZE-MAD/BCN return is adding around $300 extra to the fare.

Fare may not be booked on QR website, and due to limited availability and married segments, you might need a travel agent to help you scan for dates.