Don't know if this is fixed in the 1.18 version, but in the 1.17 version you can dupe infinite lava buckets by simply doing this:

1. Have a full inventory.
2. Spam right click on the Lava Spring with an empty bucket.

Filled lava buckets will appear out of nowhere each time you right click.

Lol, literally one line of code to fix. Will be in next update.

Fixed in v1.1.1.21

Hmmm, I thought I had already fixed that bug back in 1.16.5. I'll take a look.