Vanish however has been broken since.. forever. Which is different in it's own.
When you design a mechanic, to cover for a failing mechanic, that mechanic will eventually fail. Fixing the original mechanic was the proper way to go about doing it, but somewhere some special lil' feller decided "INO! Lets have tanks do more damage instead of trying to tweak threat numbers per spell. Yup that should fix it! /nod"
@The guy above me: During Cat, the only time I lost threat in multi-mob situations was ZA, and that was the Lynx gauntlet because I'd get stunned and couldn't hit anything until it was over. Maybe if you were a proper DPS, you'd ramp up your abilities that need ramping (SW:P, DP, VT) and THEN start with the AoE DPS you would have less of an issue, if you kept having issues then it was simply a bad tank not doing their own job properly.