Mangrove tree's roots turn flowing water into a water source block.

Have some flowing water blocks around the mangrove sapling. Bone meal it until it grows up. Notice how the roots replaced flowing water with waterlogged roots, despite flowing water being unable to waterlog a block.

This behavior is different than other areas of the game that have this occur. One example is if a tree grows leaves into an area that has flowing water. As expected the leave replace the flowing water and no water sources are created or neither are the leaves water logged. This leaf behavior is what we would expect which means the changing of flowing water to waterlogged roots is the unexpected behavior.

Expected behavior:
Roots shouldn't turn flowing water into a water source.
Actual behavior:
Flowing water turns into a full water block (waterlogged roots)