How to reproduce

1. Create a cleaning shulker box objective:

   /scoreboard objectives add cleanShulker minecraft.custom:minecraft.clean_shulker_box "Shulkers cleaned"
   

1. Display the resulting score:

   /scoreboard objectives setdisplay sidebar cleanShulker
   

1. Grab a caudron, fill it with a water bucket; and grab an undyed shulker box.
2. Click the cauldron with the undyed shulker box.

Expected behavior

The undyed shulker box is not cleaned: the score does not increase, and the cauldron water level remains the same. This is the current behavior with undyed leather armor.

Observed behavior

The undyed shulker box is considered cleaned: the score has increased and the cauldron water level has decreased. This permits to undefinitively undye a shulker box as long as you have water.