After looking at some log reports, posters on the EJ forums realized that Languish is working like Ignite as expected, but the damage currently has a 75% resist rate. The theory they came up with was that Languish's Spell rank was so low that it received the maximum resist rate against Raid Level bosses. This theory was confirmed by Ghostcrawler in a post on the official forums.
The spell level of Languish (the tier piece proc) is too low, causing an unintended high level of resists. We can hotfix this.
This is one of the few occasions where we should be thankful for a bug. The only reason we found this now was because a couple of players took advantage of a bug that allowed you to reset your Raid ID by transferring servers. This allowed them to run ICC multiple times in the early weeks of 3.3 and they were able to get the badges necessary to complete the set. Hopefully this hotfix will be in before the set bonus becomes available to many moonkin next week.
I want to take a moment and say congratulations to Murmurs for becoming the new druid blogger at WoW.com. For those of you that might be wondering, I did apply for the position also. However, I thought my chances at being chosen were a long shot at best. I was sure that my fairly narrow focus (Moonkin PvE) and loose relationship with grammar would exclude me from the job. Finding out that Murmurs is the one that was chosen makes me even less surprised.
His posts won't start for another few weeks, but I am sure they will be as insightful and math as some of his forum posts are. Just make sure to comment and call him an idiot who knows nothing about Moonkin. It's the only right thing to do when commenting at WoW.com.