Description:

Somehow the raid mechanic (presumably) can be used to dupe entities in the nether. This has been observed to to duplicate villagers, ghasts, zombie pigman & minecart with chest and thus any items inside of it. This behavior has been observed in snapshots 19w12b (no footage) and 19w13a (footage below).

What I expected to happen:

Case 1: Raids can't be started at all in the nether and don't consume the bad omen effect (at the moment they just take the bad omen effect. Also, multiple boss bars can appear by entering the nether through the overworld with a bad omen effect while another raid is already "started").

Case 2: The entities in the nether don't duplicate.

What actually happened:

Entities were duped in the nether after messing around with the raid mechanic.

Reproducing the bug:

I've published a hidden video on youtube showing the process (link below). Note that the process is quite unreliable and I've only seen it happen three times (of which two times unintentionally). Perhaps it has something to do with the amount of entities. More raid waves can be sent from the overworld to the nether to potentially increase the chance of the bug happening.

Link to footage: https://www.youtube.com/watch?v=t4miRFxppY0&feature=youtu.be

The first four minutes has some background noise from an open youtube video.

Timestamps:

0:00 to 0:10 - 1 Minecart chest full of diamond blocks is seen. The used setup is displayed.

0:10 to 2:00 - Using the bad omen effect to create multiple raid boss bars in the nether which was presumed to be the cause of the bug.

2:00 to 5:00 - Waiting for all of the raid waves to enter the nether.

5:00 to 5:05 - Failed attempt at recreating the bug. Here clearly 1 villager is seen in the "pen".

10:35 to end - Successful duplication of entities in the nether