Last patch changed so these overwrite each other trying to get a answer if this is intended or a bug and can't get a response post your thoughts its a hassle but still doable.
[48581/16374] Third Spire of Divinity IV Classes: CLR/254 Skill: Abjuration Target: Caster Group, MGB: No AE Range: 100' Resist: Beneficial, Blockable: Yes Focusable: No Casting: 0s Duration: 90s (15 ticks), Dispelable: Yes 2: Increase Melee Mitigation by 5% 4: Absorb Melee Damage: 4% 5: Absorb Spell Damage: 4% 11: Increase AC by 120 Text: You focus on the third spire of divinity. This ability, when active, will increase the survivability of everyone in your group. Additional ranks increase the durability of your group even more. [45750] Merciful Shield Target: Single Range: 100' Resist: Beneficial, Blockable: Yes Focusable: No Casting: 0s Duration: 3m (30 ticks), Dispelable: Yes 3: Cast: Recurrent Merciful Shield on Fade 4: Absorb Melee Damage: 100%, Total: 187500 Absorbs #4% of incoming melee damage up to @4 total damage. Triggers *#3%N after this effect fades. The spell effects share the same slot (4) so that's probably why Merciful Shield overwrites Third Spire. Third Spire does not overwrite Merciful Shield because its Absorb% is much weaker, however attempting to cast it on a target with Merciful Shield forces a recast timer. As Third Spire hits the entire group, though, it's not a complete waste as only 1 target in the group is likely to have Merciful Shield (though that target is probably the one you wanted Third Spire on to begin with). Maybe there is a better slot for it (not 2 though, because that is what the Warrior BP uses for its similar effect), but if this is the only conflict Merciful Shield has, I can live with it. The usefulness of Third Spire for raiding clerics was reduced considerably when it became limited to the caster group only (is no longer targetable and can no longer be cast on those outside of group) and though the AC boost is nice, the other percentages have been languishing for several expansions. Also, though Merciful Shield is very powerful, it doesn't really last that long on a tank taking meaningful damage from a raid mob (10 sec tops, maybe) and with its somewhat unique icon (the bard banjo-looking thingy) it should be easy to avoid casting Third Spire on a tank that has it. Of course, another cleric might cast a Merciful Shield on your tank even if he didn't have it at the time you cast Spire, but if that happens, your tank probably would want the Merciful Shield more than the Spire because the cleric wouldn't have wasted a 10 min recast effect unless she thought the tank was in danger of dying.
[45813] Roaring Shield Target: Self Resist: Beneficial, Blockable: Yes Focusable: No Casting: 0s Duration: 3m (30 ticks), Dispelable: Yes 2: Absorb Melee Damage: 50% over 25000, Total: 750000 Text: You guard yourself with the sonic waves of your shout. Absorbs #2% of incoming melee damage that exceeds $2 points per hit for up to @2 total damage. They are "similar" (the meaning of which is "resembling without being identical") in the sense that they both absorb melee damage, though the cleric effect absorbs all incoming melee damage (100%) up to its cap and the warrior effect absorbs half the damage over a certain amount up to its cap. I also never said they couldn't stack, though I think it's a "superficial stack" because a warrior with both on him won't use up his Roaring Shield if he's absorbing all melee damage because he has Merciful Shield on him.
True, but, wouldn't the less useful effect kick in once the more useful one is used up (~10 seconds per poster above)?
I'd assume so, that's why I used "superficial" (which implies that they don't function at the same time) to describe the stack, though maybe "visual" or another adjective might be better. "Stack" alone implies that they are working together or are additive, but in this case, one effect takes precedence until it is consumed/fades.