Filtering broken for buffers who has more 2 buffs (or more 1 long time buffs), IMHO. It's 2 classes only (pala and priest), therefore blizz havent big reaction from players and didnt fix it in last patch :-(
And just for fun http://forums.worldofwarcraft.com/thread.html?topicId=3881784980&sid=1
I think it affects all classes, but not consistently. On my warlock for example, I suddenly see many buffs while filtered, so definitely not only a paladin/priest problem.
I really hope that regardless of UnitBuff being fixed, some form of custom buff/debuff filtering will make it into agUF. Blizzard's filter is a completely useless piece of crap that only someone in deep hangover could have dreamed up (showing Unending Breath but not Blood Pact? great implementation). I wish UnitBuff stayed the way it was before, without a filter argument, would have made people implement their own custom filters and solve the problem in an infinitely better way. But like this, is easy: "you don't like the aura filter? leave me alone and complain to Blizzard, is their function".
Even agUF, since it's inception, doesn't rely on it when it comes to Weakened Soul and has a special case for it when filtering debuffs. The only unit frame addon I know that deals with aura filtering decently is Pitbull, and does it by calling UnitBuff without filter enabled. Even Pitbull could be improved though, e.g I wanna see Mortal Strike when I'm playing a healing class even though I can't cast it.
I've been running modified versions of agUF forever, for the specific aura issues, and I'm quite tired of having to put in the modifications each time an update happens. Hopefully andreasg or someone else will add custom buff filtering and end relying on the abomination that is the Blizzard aura filter.
This is well on it's way to being a full solution. The buffs whitelist just needs to be changed into a two dimensional dictionary, like filterBuffs[playerclass][buffname]. That way it will work for every class no problem. Unfortunately I'm too lazy to populate a list of every buff for every class, so I'll leave that to someone else. :P
Such a list was made by ckknight for Pitbull, look into the aura module, so you can probably take it from there. Though I don't know about license, I see Pitbull is under GPL and no explicit license for agUF, and I've no clue how this works.