Summary

Since git-Spigot-db6de12-4ac2347, entities that are pushed into a nether portal then become non-interactable (i.e. no left or right click events recieved) until either:

• The player reconnects
• The server restarted

The console will also print a message similar to Keeping entity EntityHorse that already exists with UUID 30cd14f2-916f-4162-9d56-23f9cf828f91.

Possibly related; after updating, our production server started spamming similar errors on startup and during play.

Reproduction

1. Setup a fresh Spigot 1.8.8 git-Spigot-db6de12-4ac2347 instance with creative gamemode
2. Create a nether portal
3. Spawn a horse, and then push it into the portal
4. Observe the console emits a warning about already existing entity
5. Follow the horse into the portal
6. Attempt to hit or right click the horse. Observe it does not react to either (but right clicking will reset camera, as if trying to ride horse)
7. Disconnect and reconnect
8. Attempt to hit or right click the horse. Observe both actions now work as expected

Testing

The above reproduction was tested on:

• Live server: git-Spigot-db6de12-4ac2347, 29 plugins - reproducable
• Local server: git-Spigot-db6de12-4ac2347, no plugins - reproducable

Workarounds

Any of these will fix affected entities:

• Rollback to a previous version of Spigot, e.g. git-Spigot-db6de12-18fbb24
  • We had to do this for our production server. Rolling back had no adverse effects.
• Disconnect and reconnect
• Exit and re-enter the nether world
• Restart the server

Footnotes

• This bug was discovered by a player on my server