"Mass Dispel should again prefer dispelling targets that have magic effects that can be dispelled."
Not sure if I got it right, but does this mean it will prio normal buffs? so if I havnt cleared a mage of all hes buffs, my MD will dispell hes normal buffs before the ice block?
Sounds to me like MD was dispelling targets that had nothing on them over people who actually had things to dispel, so this is more of a bugfix than a mechanics change.
No, it means that is will now prefer actually dispelling things in a large group, versus trying to dispel people who don't have anything that needs to be dispelled. Like on Warlord Zon'ozz, if you Mass Dispel when the Disrupting Shadows is applied, even if everyone is in a group and less than 10 people have it, it would still "miss" people.