Red Harvest does not confer the empowerment buff after using it at 10 stacks whether or not it lands a killing blow.
Steps to reproduce the Bug:
Use Red Harvest at 10 stacks on an enemy (killing blow or not).
Expected Result:
Should confer the Empowerment buff when used on an enemy at 10 stacks. Should have extra duration when used as the killing blow. Buff should be apparent from increased AC and extra regeneration.
Actual Result:
Empowerment buff is not present in any circumstance.
Screenshot(s)
The first screen shot shows before using Red Harvest. I'm level 15 (so already have 1 passive regen) with 14AC base. I already have 10 stacks ready to use.

In the second image, I have used Red Harvest to kill a badger with my 10 stacks. I gain all the other benefits of killing a target with a 10 stack Red Harvest except for the empowerment. My AC is unchanged and I still only have 1 passive regen (from Hemo levels). I should be getting 3 AC, 2 more Regen, and 4% physical immunity.

Additional Information/Notes