Primordius dispels are a tricky task – you want to be careful you aren’t dispelling away positive effects when they are stronger than the negative effects or offset each other, because when you dispel, you dispel all positive and negative effects. (Read our Primordius Healer Raid Guide here)
However, raids had discovered a few tricks to make dispelling much easier, by utilizing dispels that only dispelled the negative while leaving the positive. But Blizzard caught on and issued a hotfix that will prevent warlocks (with Sear Magic and Singe Magic via Fel Imp) and Priests (Mass Dispel) from being able to do this.
During the Primordius encounter, spells which dispel a single harmful effect (Sear Magic, Single Magic, or Mass Dispel) will no longer work if any of the positive effects are active on the target (Improved Synapses, Keen Eyesight, Thick Bones, Clear Mind, or Fully Mutated).
Dispelling on this fight is pretty easy, with raiders simply calling out for single target dispels when negative buffs outweighed the positive ones. It saves healers from having to try and guess who needs dispelling… however it won’t prevent those people from being annoying by dispelling helpful effects of fellow raiders they want to piss off.