Update: As predicted, Valve deployed a patch ASAP. The bug is now fixed. Sorry, Dire. You're back to stacking your own Ancients now.
Original: Yesterday, Chris questioned whether Dota 2 Reborn was ready; suggesting that Valve's lane-pusher has gone back to beta. Maybe that explains this: a major balance-breaking bug that has been introduced into the latest version of the game. Dire's Ancients—the big, stompy mobs lurking near the Roshan pit—are auto-stacking without any intervention.
Stacking is supposed to be a trick that support characters who aren't me can do. They pull the Ancients out of their jungle camp just as their spawn timer ticks over. The game, thinking there are no Ancients in the camp, spawns new ones. The original Ancients return to their position, and now there are two stacks available for gold-hungry heroes.
Currently, Dire-side Ancients are spawning automatically—without the need for player intervention. A gif posted to the Dota 2 subreddit shows this in action. This, naturally, is a major issue for the game's balance. It's a huge advantage to the Dire; and specifically to the heroes that can easily eat a big stack of Ancients. Things can quickly get out of hand:
It's a big enough bug that joinDota League has announced that all its matches are suspended until things are fixed. Given the seriousness, that will likely happen soon. Until it does, definitely avoid playing ranked.