The Bug:

minecraft.used:minecraft.bucket doesn't increase when taking powder snow, lava, or water from a cauldron using a bucket.

Steps to Reproduce:

• Create a scoreboard objective for tracking the use of a bucket and set it to display on the sidebar.

/scoreboard objectives add UseBucket minecraft.used:minecraft.bucket
/scoreboard objectives setdisplay sidebar UseBucket

• Take some powder snow, lava, or water from a cauldron using a bucket.
  →  Notice how the scoreboard doesn't increase.