When placing water on the ground, sometimes the server will not acknowledge the water being placed.
After being updated by a second water source block water that was placed and not rendered/responsive becomes active.
What causes the issue to happen is currently unknown.
[Here is a link to some tests|https://www.youtube.com/watch?v=jeHUbzqCP38]
Are these full stone blocks or stone slabs that are waterlogged by right-clicking them with the bucket (see MC-131021)?