I was in RA and I was a Prot. monk using Life Sheath. On the other team there was a Touch ranger. I had won like 5 in a row acting as a tank with Life Sheath so that no damage got threw. When the touchie got in touch range i threw up LS and his first Vampiric Bite went right through adn I took the damage. I looked back up at my enchants and LS was still on then he hit me again with Vampiric Touch and that went right through. I looked again and LS was still up. There is a bug where those 2 skills (possibly more) are not negated by LS. That angered me because I was on a roll then we lost. Anet needs to fix this.