Strange bug?

[donken6]

Howdy

I altered Shadow strike spell the following:

atk spd factor: 0.5
Decaying dmg: 75
Initial dmg: 752
move spd factor: 0.9
cast range: 220
cast time : 0
duration : 10s
made a custom copy of buff Shadow strike

Can somebody understand and tell why or how it now is a instant kill? The target has well over 10k hp (and no, I dont have cheat on.. )
Also checked extra time that I dont have any strange trigger active regarding this spell..

 

[Duckfarter]

I believe its like this: Cast time, amply named, is the period for the dot damage. So 0 casting time means dot damage is dealt every 0.00 seconds for the duration of the spell.