Snow neither forms nor melts at block light level 11

Snow layers are unable to form or melt at light level 11, this seems to be an off by 1.

Simple tests:

1. /fillbiome ~-20 ~-5 ~-20 ~20 ~10 ~20 snowy_plains
   /fill ~-16 ~-1 ~-16 ~16 ~-1 ~16 glass
   /fill ~-16 ~ ~-16 ~16 ~ ~16 glowstone
   /fill ~-15 ~ ~-15 ~15 ~ ~15 air
   /fill ~-11 ~ ~-11 ~11 ~ ~11 snow
   /weather rain

   → The snow does not form 1 block further than the fill command, no matter how long you wait

2. (from same position as the other commands) /fill ~-12 ~ ~-12 ~12 ~ ~12 snow
   → The snow spawned in by the command does not melt, no matter how long you wait