I played a game (#939588 on oregon) where I Discipled an Overlord (choosing Laboratory). According to my understanding (and this http://forum.dominionstrategy.com/index.php?topic=16199.0 thread), I should have received a Laboratory from Disciple, but I got an Overlord:
Turn 13 - Ingix
I plays a Disciple
I plays an Overlord
I plays a Laboratory
I draws a Copper and a Plaza
I plays an Overlord again.
I plays a Laboratory
I shuffles their deck.
I draws a Laboratory and a Menagerie
I gains an Overlord