Water not Spreading infinatly in 2 deep areas as expected

Is there a source block below the area where you expect the source block to form?

The water is a natural underground lake. Water spreads normally in the 1 block deep areas but not where it is 2-3 bocks deep. I though that a few updates back they made it so water spreads and fixes itself in areas that are more then one block deep.

The block underneath where the water is spreading too must be a source block as well.