When dropping a honey block on a honey block you can see though both honey blocks and through water. I just found this today and it may also work with the border but i havent checked.

What I expected to happen was...:
to see a 'transparent' block be dropped on honey and not be see though or see though water with n discolouration

What actually happened was...:
i could see though the placed honey blocks from the honey block entity. and see through water

Steps to Reproduce:
1. place any amount of honey blocks vertically
2. drop another honey block on top of the pillar of honey blocks
3. look at the honey block entity

4. angle yourself to see water clearly through the dropped honey block entity