It's currently being worked on I believe, but would not be surprised if other problems are appearing as a result which also require fixing and those again cause other problems which is extending the time needed to bring the patch to a point where it solves at least the majority of bugs without introducing worse ones.
I've seen MMO's where patches/updates have caused major problems and have had to be patched or retracted and the patches for the 'bugged' patch have themselves caused other problems, hence why I'm saying what I'm saying and am not too worried that it's taking a bit of time.