Have priests and shaman shield me regularly and never had a problem.
Generally they will only shield me on big or hard hitting mobs before I pull to ease there healing load at start so they dont drag heal agro. For a priest healer its generally binding heal, shield then I pull this generates very little agro to them.
A typical example is the 2 bog lords in H-UB I can only get 1 with my AS until the 2nd is cleanly in consecrate the healer cant really heal it means I can suck a few of blows from 1 lord before needing a heal.
I dont get the whole mana thing why would a healer bother to shield you on a small pull where you arent going to take much damage?
I will make one comment they have to shield you before you pull or much later in the fight they cant do it just after you pull because it does seem to generate a pile of heal agro which if you dont have a good lead means they go for your healer.
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