The Bug:

Filling bottles with dragons' breath also uses items held in your offhand.

Steps to Reproduce:

1. Hold some glass bottles in your main hand and a fishing rod in your offhand by using the commands provided below.

   /item replace entity @s weapon.mainhand with minecraft:glass_bottle 64

   /item replace entity @s weapon.offhand with minecraft:fishing_rod

2. Summon an ender dragon that will breathe on the ground by using the command provided below.

   /summon minecraft:ender_dragon ~ ~ ~ {DragonPhase:5}

3. Collect some of the dragon's breath using the bottles, and as you do this, watch both of the items held in either of your hands closely.
4. Take note as to whether or not filling bottles with dragons' breath also uses items held in your offhand.

Observed Behavior:

Filling bottles with dragons' breath also uses items held in your offhand.

Expected Behavior:

Filling bottles with dragons' breath would not also use items held in your offhand.