STEPS

1. Go to a biome where water doesn't normally freeze (e.g., plains)
2. Create a 3x3x1 puddle of water surrounded on all sides by torches.
3. Wait until winter

EXPECTED

The water doesn't freeze because the light level is greater than 11 (see Usage on official wiki).

ACTUAL

The water freezes no matter what the light level.

NOTE

This makes for an especially annoying experience when trying to maintain crops (i.e., the water freezes and the earth dries out), or maintaining Animania animals (i.e., the water freezes, and they get thirsty and die).

Our code does check for the light level (It's pretty much ripped straight from vanilla), and as such, I can't reproduce this. Make sure the water blocks in question are actually at a light level of 10 or above, which is what the ice/snow forming checks for.