Two water sources cannot create an infinite water source onto a waterloggable block

The bug

If you have two water sources next to an air block, they will create an infinite water source between them. However this doesn’t work if they are next to a waterloggable block. This allows you to get air underwater, like before the aquatic update.

How to reproduce:

1. Build a cross underwater made with non-waterloggable blocks
2. Replace the block in the middle with a slab
3. Break the 4 adjacent blocks on each side of the slab
   The slab won’t get waterlogged and you have air underwater.