Divine Guardian (Tier 4 of Prot Paladin tree) has a known bug where the Paladin will keep abosorbing damage even after Divine Shield is no longer active. There's a few other posts on this website that say things like, %26#8216;avenging wrath with it up' (no longer causes the desired effect) and other similar ideas but none of them guarantee it.
Long story short when you cast divine shield, if you macro it off nigh-immedietly, it will always have the buff from DG remain on you. Although it's nothing insane or noteable, we tried this last night on Sapphiron and the Prot Paladin (who wasn't currently tanking) was taking 30% from everyone coming from Sapphiron's aura and it lasted until he died.
by Grizzam