The bug
Boats, lava and water buckets and lily pads (all methods calling Item.rayTrace(World, EntityPlayer, boolean)) can be used / placed through entities meaning you do not have the block you are placing them on focused.
This is inconsistent with normal block placement and additionally creates unexpected behavior because right clicking your pet to make it sit while holding a lava bucket will place the lava under your pet.
How to reproduce
Spawn for example a cow in front of some blocks
Right click the cow with a lava bucket
→ ❌ Lava is placed behind the cow
Linked issues
Attachments
Comments 19
Affects 19w46b & 1.14.4.
This bug could kill mobs and players as well as burn down structures accidentally by using lava buckets, which may lead to frustrating situations for players.
I would increase the Mojang Priority value because of this, although I don't know the technical difficulties of fixing this bug.
Affects 1.15-pre1.
Example of accident when playing:
[media]
Can confirm in 20w48a.
Can confirm in 21w03a.
Can confirm in 21w06a.
Can confirm in 21w07a.
Can confirm in 21w11a.
Can confirm in 21w13a.
Can confirm in 21w14a.
Can confirm in 21w15a.
Can confirm in 21w17a.
Can confirm in 1.17.
Can confirm in 1.17.1.
Can confirm in 1.18.1.
Can confirm in 1.18.2.
Can confirm in 1.19.
Can confirm in 1.19.2.
Can confirm 1.21.4 Pre-release 3.
Confirmed (also in 1.12-pre4). Might relate to MC-4381 (which was resolved as intended for some reason).