The Wraith bring a Pegasus (new model) Stargate close to Earth. It has a Pegasus DHD too. Since it has a DHD, it becomes primary, so it will receive any incoming wormholes. We learn that because they are a newer model, the presence of a Pegasus gate also prevents a Milky Way gate from dialing out! This was first discovered at the Midway Station, which has both types, neither with a DHD. the problem was solved with appropriate software, but of course we can't do that in this case since we can't reprogram the Wraith's stargate right now.
Then it turns out that as it is, a Pegasus DHD isn't much use in the Milky way since the coordinate system is all wrong, but a couple of minutes of McKay programming fixes that. Then it all gets blown up and we go back to the way things were.