Summary:
Bought sentry ward to deward an observer ward. It was the only source of true sight in the area. Used plague ward to deward the observer. Plague ward killed the observer, message popped up saying observer was killed and bounty was given. No bounty was received.

Repro Steps:
1. Find enemy observer ward spot
2. Buy true sight
3. Apply true sight to area where enemy observer ward is
4. Summon plague ward (may or may not work with other player controlled units, but in this specific case, it was veno's plague ward).
5. Plague ward kills observer ward
6. See observer ward killed message pop up.
7. Notice only a +1 change in gold (from passive gold income).

Result:
Provided true sight over observer ward and then killed observer ward but did not get bounty.

Expected Result:
The player that provides true sight over observer ward should get bounty regardless of who/what had the last hit on the ward.

If it helps, this happened in the match: 5287716800
Timestamps: 9:23 in-game time and 9:47
Also note these screenshots: http://prntscr.com/rf373w and http://prntscr.com/rf37gs