When using a bucket of water on water logged blocks it places the water inside the block even when shifting. The intended result works properly with the cauldron when you hold shift it will place the water on the corresponding side instead of inside the cauldron. A few examples of blocks you can't shift click to place the water next to it are (leaves, fences, ladders, most water logged blocks).

To get same result place a leaf block and hold shift and click with bucket. you'll notice the water will always place inside even when shifting creating annoying situations.