soul breaker's pride of kamael

whenever i use this skill it stays for like one second and then gets removed, whats up with it? also it should stack with the adv guide buffs because i saw an another soulbreaker who could use it with full buffs but we couldn't figure out what caused mine to not work, my only guess is that he was on sub-class while mine was the main class but it's still a bug in that case...