Gravebind Rope Cuffs another bug. Steals ability of party members to get mana on kill

Gravebind Rope Cuffs makes mana on kill for party members unusable. In short, if party member kills minion while next to you, he will not trigger any on kill effects (the one we tested mana on kill)

How to reproduce:
1) Have one character with mana on kill feature.
2) have another person with Gravebind Rope Cuffs
3) Be close to each other, mobs that are killed won't return any mana.

This sounds like what the "instead" at the end of the modifier would cause to happen, yes. How is this a bug?