Cannot reproduce on spigot 1.20.1

ya, the above code works, i said it did and striked my statements out in order to state that what i originally said (the striked through sections) is incorrect. the Wolf class however does not seem to be working correctly though. Although i haven't fully experimented, i can't figure out what is happenning, atm i am under the impression though that Tameable is indeed working correctly, however i am skeptical about Wolf. I am confused about it now, im not sure what's going on so i'm going to just avoid using specific child classes of Tameable and just use Tameable instead. I don't know enough about minecraft/spigot internals to investigate this so im just going to stop commenting on it.

I used your above code exactly and was still able to correctly set the owner of multiple passive wolves. 

The only inconsistency was if the wolf was aggro'd, you could take ownership and make it sit, but once it stood up you could no longer make it sit until you died and it lost aggro. 

EDIT: To clarify, I used the above code and changed Tameable to Wolf. 

it still doesn't appear to fully refresh until server restart.

@EventHandler
public void onPlayerInteractAtEntity(PlayerInteractAtEntityEvent evt) {
     if(evt.getHand().equals(EquipmentSlot.HAND))
          if ((evt.getRightClicked() instanceof Tameable)) { 
               Tameable ent = (Tameable)evt.getRightClicked(); 
               if (ent.isTamed()) { 
                    if (!ent.getOwner().equals(evt.getPlayer())) { 
                         ent.setOwner(evt.getPlayer()); 
                    } 
               } 
          }
     }
}

code should allow anyone to interact with tameables , Since 1.8 the new owner ends up getting desynced or something within the server logic and doesn't right itself until server restarts.-

nevermind, it does work with Tameable, but Wolf class doesn't work?

the above code works, however but if you replace Tameable with Wolf then it is broken it seems... Odd but that's fine, sorry for the many edits, i got confused with the behavior i was seeing in 1.13.1.

I cannot re-create this issue. I was able to set the owner through a plugin using various accounts and it always correctly updated to the new owner.

CraftBukkit version git-Spigot-2440e18-4228a56 (MC: 1.13.1)

API version 1.13.1-R0.1-SNAPSHOT

Tested using this tiny sample plugin code. 

@EventHandler
public void onEvent(PlayerInteractEntityEvent event) {
    Entity entity = event.getRightClicked();
    Player player = event.getPlayer();

    if (player.isSneaking() && (entity instanceof Tameable)) {
        Tameable tameable = (Tameable) entity;
        tameable.setOwner(player);
    }

}

I also ran a test using Wolf directly instead of casting as Tameable.

I'm bumping this up to major priority because this is a good time to investigate this bug.

still not working correctly as of

CraftBukkit version git-Spigot-b32c8f8-4d3bf20 (MC: 1.11.2)

API version 1.11.2-R0.1-SNAPSHOT

Edit:
Just noticed I was more than 30 versions behind (oops) but this issue still exists as of:
CraftBukkit version git-Spigot-af982fc-0df416d (MC: 1.10.2)
(Implementing API version 1.10.2-R0.1-SNAPSHOT)

Also, Ocelots have the same issue