I am not sure if this a bug or intentional, but spring blocks cannot be generated over existing spring blocks. This can create some issues such as creating "holes" in larger bodies of water. I am aware of stacking blocks such as dirt or sand under it to fix it but this is not a real solution.

There was a mod that addressed this issue a few months ago:

www.minecraftforum.net/topic/1197409-water-spring-propagation-fix/