Negative values in spells

I made a "Healing Dart" spell based on Shadowstrike; it is supposed to do 100/200/300 damage and then -50/-100/-150 damage per second for 4 seconds.

The problem is, when I cast it on someone their health shoots up like a rocket and stays at max no matter how much they get pounded on, until the 4 second duration is up.

Data - Decay Power: 3.00
Data - Decaying Damage: -50.00
Data - Initial Damage: 100.00
Stats - Duration - Hero: 4.00
Stats - Duration - Normal: 4.00

What is wrong here? I tried setting it to -1.00 decay damage, didn't make any difference. Set initial damage to 1000, and it doesn't even kill someone with 12 hit points, so fast does it heal.

Decay power: What does it do?

I don't know, but try setting it to -3.

what did u set the casting time to? if u have changed it then try changing it to 1 or 3 or sumthing, i think this might work....if u havent changed it, then i have no idea whats happened