Upgrade - Damage Loss Bonus

I have a bounce attack upgrade. I can upgrade the number of target, but when I try to modify the damage loss, strange things happen.

My damage loss is set to 0.5 on the unit. If I upgrade the damage loss, which can only be upgraded with integer bonus, the first enemy get hit for full damage, the next receive no damage and the next receive full damage, etc. I guess it has something to do with the fact that the damage loss should be 50% but when I upgrade I can only give bonus of 100% at a time.

Am I doing something wrong ?

Are you doing this in the object editor, gui, or jass? Please post your soure code, or explain which ability/object fields you are editing.

This is for bouncing attacks such as huntresses, but I never came across this problem...

Object editor. The only thing that is triggered is the research of the upgrade when my hero learn the ability, but that's working as intended.

On the Unit:
I use Combat - Attack 1 - Area of Effect (Full Damage) at 400
I use Combat - Attack 1 - Damage Loss Factor at 0.50
I use Combat - Attack 1 - Weapon Type at Missle (Bounce)

On the Upgrade:
I use Data Effect 1 at Attack Target Bonus Count
I use Data Effect 1 - Attack Target Bonus Count Base at 1
I use Data Effect 1 - Attack Target Bonus Count Increment at 1
I use Data Effect 2 at Attack Damage Loss Bonus
I use Data Effect 2 - Attack Damage Loss Bonus Base at 1
I use Data Effect 2 - Attack Damage Loss Bonus Increment at 1