I've noticed this since just before the anniversary event: the cages in Northern Grasslands (Khitai Godslayer expansion area) have become invisible. One such cage is in Chow across from the entrance and has a captive Zhang-Zin inside, which is visible, but the cage around it is not. Not a big deal, since its not a quest item, but another such cage is a part of Wolves of The Steppes "Running down prisoners" quest, and it is gone along with all its contents - completely empty land in its place, which has "invisible barrier" i cannot go through. Approaching it does spawn the quest "prisoners", but on the visible empty piece of land, which is extremelyannoying for me (before I used to at least see where i needed to go to start the quest, and sometimes avoid that spot, if more time was needed, like in case someone already spawned prisoners and the cage was empty and needed to reset). There are few other Khitai areas that have similar cages (quest objects), such as Kara Korum's Temple of the Basilisk and the town of Gun-Hai in Chosain, but those will still show up with no graphical glitches.
My system is:
Processor: AMD Phenom(tm) II X4 965 Processor (4 CPUs), ~3.4GHz
Operating System: Windows 7 Ultimate 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_rtm.101119-1850)
DirectX Version: DirectX 11
Card name: ATI Radeon HD 5700 Series
RAM: 12 GB
Picture 1:
http://i43.tinypic.com/34jb05l.jpg
Picture 2:
http://i42.tinypic.com/20svex3.jpg