[Legolas]

Some spells like Greater Sanctuary are indeed bugged. I vaguely recall Premonition or Shadowshield or similar faltering for no apparent reason as well, though it's old second-hand knowledge so I can't give you all the ins and outs of it. The theory at the time was that the order in which you cast your buffs had something to do with the effectiveness of certain individual spells. No doubt the crowds on the hardcore pvp servers can enlighten you.