When you cast Necro's Reaper Scythe on an enemy afflicted with Fatal Bonds, the following situations can happen:

1. Your Reaper Scythe does NOT do enough damage to kill the target - the damage you did is properly spread to the Fatal Bonds targets.

2. Your Reaper Scythe DID enough damage to kill the target - however, Fatal Bonds targets do not suffer any damage.

In other words when you Scythe a target that is under Fatal Bonds it will spread it's damage (through Bonds) only if it fails to kill the target.

I want to point out that Fatal Bonds will NOT spread damage from "instantly killing effects" like Culling Blade and Midas - but Reaper's Scythe is NOT such an effect, it is just a single target nuke.

To me this seems like an obvious bug, but i wanted to ask the bug-veterans here before making a true bug report about this.