The usual lifesteal ability is told to be stacking, if you put a different buff on it(Yes, it doesn't show one by default, but it has).
Does it matter if its on a melee or a ranged attack?
Just to make sure, are you reffering to "Life Steal (Frostmourne)"?
Last edited by PurgeandFire; 10-14-2013 at 03:30 PM. Reason: edited the title to be more specific