compose requiem skill duration

Last Lament requiem skill tooltip says - for a short fixed amount of time, and another tab says 12 seconds, when in reality it lasts random amount of time up to 12sec. getting stunned or taking damage not sure what ends the skill.

if its not a bug tooltip should explain at what condition skill turns off and cooldown is started

It also gets interrupted by charms, potions, heard someone say even music loop stopping interrupts it. This bug really makes this crossbow annoying to use. Please fix! :(