Steps to reproduce

1. Create a world with "Weather Cycle" ON 
2. Play for about 2-4 hours IRL and wait until it rains
3. Then use /weather clear or wait for about 2 - 3 Minecraft-days the rain itself will stop (Mobs on fire won't be put out, fire spreads normally), but the rain animation (including water falling down, splash particle on the ground, dark sky) will last forever unless you exit the world.

Expected result

The rain animation should stop.

Observed result

The rain animation lasts forever until you exit the world.