Minecraft 19w13a, Minecraft 1.14
When a illager captain (an illager with a banner) that spawned during a raid, is killed, it will still give its killer the bad omen effect, causing raids to never end.
When starting a raid and sending the banner carrier (spawned from the raid) to the nether you can get the bad omen effect from him. This allows the player to start a raid over and over again by sending at least 1 banner carrier to the nether.
What I expected to happen:
The banner carriers spawned from raids don't give the bad omen effect.
What actually happened
The banner carriers spawned from raids give the bad omen effect when killed in the nether (where there is no raid active).
Steps to reproduce:
1) Start a raid in the overworld
2) Lure the banner carriers to the nether
3) Kill the banner carriers in the nether (make sure there is no raid active in the nether). Each banner carrier equals 1 level of bad omen which can be brought back to the overworld to start another raid.