The Bug:

You can decrease the level of a water or powder snow cauldron, through the use of a player on fire in spawn protection.

Steps to Reproduce:

• Start a server and join it.
• Give operator permissions to yourself.
• Set the world spawn to your current location.
• Place some powder snow or water inside of a cauldron.
• Place some fire nearby and switch into survival mode.
• Remove your operator permissions.
• Give operator permissions to any person other than yourself.
• Stand in the fire and attempt to extinguish yourself through the use of a powder snow/water cauldron.
  →  Notice how you are extinguished and the level of the water or powder snow cauldron is decreased, despite it being in spawn protection.