The bug
In creative mode filling a cauldron from a water or lava bucket gives the player an empty bucket, provided they don't already have one in their inventory. This didn't happen in 1.16.5 so it's introduced in 1.17's first snapshot.
Video demonstrating the issue:
How to reproduce
Place a cauldron
Get a water bucket
In creative mode, right click the cauldron with the water bucket
→❌ Notice an empty bucket is added to the hotbar
Linked issues
is duplicated by 13
MC-275762
Bucket issue
Resolved
MC-275763
You get an empty bucket when you pour liquid into the cauldron
Resolved
MC-276147
bucket duplicate when using on cauldron in creative
Resolved
MC-234369
In creative mode, using a water bucket for a cauldron refining pot will give you a bucket
Resolved
MC-232212
Creative cauldron bucket creation
Resolved
relates to 2
Attachments
Comments 25
That is not true, in 1.16.4, you don’t get an empty bucket in creative mode when putting water into a cauldron.
Can confirm that this didn't happen in 1.16.4. Reopened.
Might still be intentional though – after filling a cauldron you might want to empty it again, and you need an empty bucket for that.
But you don't want your creative inventory full of buckets do you?
If you want to empty it, just get a bucket yourself!
It seems to still happen in 1.21.4 and with water bottles as well! This makes me believe the issue is with the interaction itself, and makes this the same issue as MC-269237
That is an intentional feature, added in 1.16, please read the changelog for more information.