Description: I had a "Shared Map" treaty with another civ. Not sure if relevant but it was another human player on multiplayer.  I found an empty continent and started exploring it.  I discovered a natural wonder. It was one of the "Deed" natural wonders that gives you Fame upon discovery.  Because I had a "Shared Map" treaty, my friend and I both received the credit and Fame for "discovering XYZ natural wonder first". This is probably a bug in itself, but it gets worse. I then claimed the territory containing the Natural Wonder using my scouting unit. Once my outpost was completed, my friend got a grievance against me (paraphrasing) "Another player claimed a territory that contained a natural wonder that you were the first to discover". I think he should not have this grievance since I was the one to actually discover the natural wonder, and he only got shared credit because he happened to have a "Shared Map" treaty with me. He never sent a unit anywhere near the natural wonder.

Attachments: a few diplomacy screen screenshots: the grievance (step 6 below), both players receiving credit for discovery (step 4 below) and the shared map treaty (step 2 below)

Steps to reproduce:

1. Make a game with 2 human players.
2. Agree to a "shared map" treaty.

3. Explore the world until one player discovers a (new) natural wonder.

4. Observe that both players get "first discovery" credit (Bug)

5. Have the "real" discovering player claim the territory containing the natural wonder.

6. Observe that the other player gets a grievance against the claiming player (Bug)

Expected Behavior: I would expect that the game would credit the discovery to the player who actually uncovered the natural wonder with a unit, and that the credit would not be shared with another player via the "Shared map" treaty. If this behavior is corrected, I believe the grievance bug would fix itself.