A water block is created in the same block as signs

I created a 3x1 hole and added a sign in one of the faces of the middle block, used a 2 buckets of water on each side with a sign in the middle, and the water spawned in the same block as the sign 

What I expected to happen was...:
i expeted this layout (waterbock / sign / water)

What actually happened was...:
what happed was (waterblock /sign and waterblock / waterblock

Steps to Reproduce:
1. create a 3x1 hole in the ground 
2. add a sign in the middle 
3. add water in the coners