Stay tuned to HKO Insider for the latest. Hopefully they'll hotfix this one right up.
Updated 11:00 p.m. EDT: Belfaire posted "We're gathering the appropriate info now. I have no ETA on a resolution, only that it'll be [fixed] ASAP." (April Fool's text removed for readability.)
Updated 12:44 a.m. EDT: Belfaire also let us know that Q.A. is working on the problem, though no fix has been announced yet. Seems they are at work on it.
Updated 1:00 a.m. EDT: Potential solution from Belfaire: "Please have your entire raid delete or rename your Interface folder and let me know here if you encounter the issue again. [One] group said that they ran without mods, but if what I think's happening is actually happening, even if one person has [an addon], it can affect the raid."