Using a water bucket on a lava filled cauldron or vice versa deletes the contains of the cauldron

The bug:
When you click a lava cauldron with a water bucket or a water cauldron with a lava bucket the contains of the cauldron before you clicked it are simply deleted and replaced
How to reproduce:

• place a cauldron

• fill it with water
  -try to fill it with lava

• the water disaprears and is entirely replaced by the lava