Well, it would appear that the information about Chaos taking over Altdorf wasn't completely true, or rather the were not completely known.
Here is a response from EA that I found over on Tobold's blog about the situation;
I think your concern is completely valid and I don't fault your original blog post. I'm not here to tell you that you are wrong. Like I said, I wanted to give you more information about your concerns.
As you correctly stated, there was a bug, since fixed, that incorrectly set the postern doors in the fortress so that players from both Realms could access the inner Fortress. This allowed them to circumvent many of the fortress defenses with a smaller force than usually necessary and do it much quicker than would normally be possible.
On top of that issue, the time required for players to capture the two fortresses had been incorrectly set to 36 hours. It is now correctly set at 12 hours. This gave those same players three times the normal time allotted to achieve their goal of capturing both fortresses. This also means that without a fairly massive force, players may be able to take one fortress with a 3:00 AM raid, but not both. Instead they will have to play into the day and the chances of a successful player defense rise with every hour that passes.
On Karak Eight Peaks, Altdorf was put into a contested state and Destruction was able to initially win this stage of the fight. However, the same forces that so "easily" defeated the fortresses were unable to defeat the Bright Wizard College and Sigmar Temple Public Quests. These quests gate access to the King, so Destruction never fully captured Altdorf. Because they could not accomplish this goal, the City was held a brief time while the Destruction players attempted, several times, to successfully complete the City Public Quest, having given up on the other Public Quests. At this point, the forces of Order gladly re-entered the City and pushed out the remaining Destruction forces.
The end result of this was that while a small dedicated group was able to make use of two incorrect settings in our game to get to Altdorf, they were unable to accomplish anything meaningful once inside the City. Now that Fortresses have been corrected to work as designed, it would take a much larger force much longer to get to Altdorf.
You have to keep in mind that a City capture is a long multi-stage process that requires all of the following elements (I will use Aldorf as my example).
1) You must capture two fortresses in Tier IV within 12 hours of each other. To gain access to a fortress you must seize and hold the neutral Tier IV zone and your opponent's zone in two separate racial pairings. Once you lock down one racial pairing, you only have 60 minutes to capture its fortress. Should you fail, then that racial pairing reverts back to a neutral state and you must begin anew.
2) You must then fight in contested Altdorf and gain control much like you would in a zone. There are two Battle Objectives, a Public Quest and opposing players you must contend with in order to accomplish this.
3) Should you accomplish the first two tasks, the opposing realm is ejected from the city. At this point you have one hour to cement your hold on the city. You must complete the Temple of Sigmar and Bright Wizard College Public Quests within the next hour. If you manage this feat within one hour, you then lock down the city for 24 hours and unlock the King. If you fail, then you have one hour before the city is re-opened to opposing Realm players.
4) If you defeat the King, then you can unequivocally say that you captured Altdorf.
It's certainly possible that a massive well-organized force operating in the dead of night could seize and hold a Capital City over the course of a great many hours. Then again, if you organize a fairly large fighting force and utilize good strategy and timing to strike quickly and effectively, you should be rewarded for that behavior.
I would be happy to answer any follow-up questions you have. Thanks for giving me the opportunity to elaborate on the City capture.
It's great to see a quick response from EA, and that it truly is an epic task to take an opposing factions capital city!