We dug into this, and we’ve determined that it is not a bug.
The tooltip says: Your melee hits have a 9% chance of allowing the use of Execute regardless of the target’s health state. In addition, you keep at least 10 rage after using Execute.
But it should say: Your melee hits have a 9% chance of allowing the use of Execute regardless of the target’s health state. In addition, you keep at least 10 rage after using a Sudden Death Execute.
We’re looking into updating the tooltip.