Weird Pest problem...Follow

So, I've encountered a Pestilence glitch a few times in the past two months or so, and I'm wondering if I'm just an idiot or if this is common.

The glitch:

I place 3 diseases on a mob and use Pest. Some of the mobs in the pack receive diseases and others do not. No mob receives partial diseases (3 or none).

No mobs in the packs are immune to frost, and as far as I know they don't shield (for example, it just happened to me when using it on a pack of Converted Heroes).

Has anyone else had this happen?

The only thing I can imagine being the cause is if each "jump" in the spell is a separate "step." Like spreading a disease from mob 1 to mob 2 is a split second faster than mob 2 to mob 3. If I were to kill mob 2 in the perfect moment, then it might stop the chain? But I have trouble imagining how that happens, since I'm still likely targetting the original mob.

Anyone else ever encounter this?

And I am right in assuming that Pest is a 1-time hit or miss, right (though I'm not sure it CAN miss, actually)? Like, it won't hit some targets and then miss at mob 4 and stop?

Like I said, I think it's happened 3 or 4 times in 2 months. Not a huge problem, just annoying every so often.

That... really sucks. But it still can't be it. 17% is the spell hit cap for level 83 mobs. Converted heroes are 80, so my 10.x% spell hit is WAY more than is needed. Realistically, anyone even slightly geared should never miss a spell on level 82- mobs. You only need 158 hit to be capped for level 82 mobs, 105 for 80s. I'm melee capped, so I'm definitely not missing spells on them.

Let me just get the obvious out of the way then -

You're talking about packs that have been clumped up after being pulled, right? As in - you don't throw your penance down while half the group is still moving? Because if it's the later, it might simply be lag issues causing your Pestilence not to reach the mobs that are hovering just out of it's range.

On another note, do you have the Pestilence glyph?

Hmmm... have you tried petitioning a GM? It might be nothing, but they might be able to confirm your theory or otherwise check if there's anything fuzzy going on in their 'combatlog'.

Also: Penance? What was I thinking? I've become a healzombie!