Cool! Actually I think I just found the base issue...
Looks like I"m using a newer version of the Mavlink library for my own QGC builds. So the problem can also be fixed by updating the library included in the QGC repo, or changing the MAVLINKPATH variable in qgroundcontrol_aq.pro to point to a newer version (eg. MAVLINKPATH = e:/lib/mavlink/include ). This would actually apply to builds for any OS. Thanks for reporting!
Yea the festival/speech stuff is vague... I've gotten it to work several times but still not really sure how!
-Max