No Ice generation when covered by fences

Even tho you can fall through a fence covering an area it is not generating ice blocks in a snow area.

What I expect to happen was:
The static water in the pond will generate ice blocks

What actually is happening:
No ice blocks are generated

Steps to reproduce:

• In a Snow Biome go to a pond (or create one).
• Cover the whole pond with fences (sides and above)
• Wait some time