You can see through the water in a small gap when a shulker and shulker box is right above a water block.

Steps to Reproduce:

Step 1

Place a shulker and/or shulker box right above the water

Step 2 

Witness the bug unfold

Observed Results:

You can see a gap between the shulker and shulker box

Expected Results:

You shouldn't be able to see through the water