Water in waterlogged stair does not flow if stair is removed

If a stair is waterlogged with all flowing sides blocked, then the stair is removed, the water will not flow.

 

Steps to reproduce:

Make a 3x3 doughnut of waterlogged stairs (back facing outwards) and remove a corner block or

Place a waterlogged stair, surround all sides except the back and top with another block, and break the stair