Twice tonight, and once in the past month once again in my runs to obtain Baron Rivendare mount the gates(both inner and outer) to the Slaughter House (the building in which he resides) stay closed after the Black Guard Sentries are killed.
I kill the sentries inside the outer gate so that I am in the area with the steps down to the room Baron Rivendare resides in, and after they die the front door shuts and the lower door to Baron Rivendare also stays shut leaving my toon trapped until I can hearthstone out.
I only report this as a bug because in the many times I have run this instance in the past the lower door had opened once the sentries were dead.
In addition, tonight I tired to stay outside of the outer-gate to kill the sentries. After that I killed the swarms of non-elite zombies that flooded into the square in hopes that this would open the gates. But to my displeasure this was not the case and the doors stayed shut. However as an added bonus I observed that the gate to the square in which the slaughterhouse resides was also sealed shut. This once again had forced my character to hearthstone out of the instance.
At the moment I cannot try to get the mount he drops, is there some mechanic that I am bugging out due to the brevity that I am killing the mobs? I think not because this had not happened in the past 50+ runs I have done.