to add.. i was doing a quest whilst leveling my dk... my Dark Succor glyph was actually not healing for 20% of my hp after a kill even though it would proc, instead of healing the 37k ish hp it should have healed it was healing closer to 18.5k.
Although, im not sure if i actually got exp from the mobs (it was the wall quest where you need to kill the tauren like mobs, and gather the oil barrels) but the DS icon would show, yet not heal properly.
I would've normaly dismissed it, but since it's Mione i actually went and read the tooltip.
"Focuses dark power into a strike that deals 392% weapon damage plus 2,932 to an enemy and heals you for 20% of the damage you have sustained during the preceeding 5 sec (minimum of at least 7% of your max health). This attack cannot be parried."
So if in the preceeding 5 seconds i sustained more than 35% of my HP in damage it should heal for 20% of that, otherwise it will heal for 7% of my HP.
considering i was purposely sitting while being hit by 2 elites so that they would crit me, and that they took around 50% of my HP in ~5seconds shouldn't it heal for 20% of that (so 10% of my total hp) ? The heal never went up even a single point.
It also happened yesterday during our raid, and I'm pretty sure i was losing over 35% of my hp every 5 seconds.