When the game renders celestial objects in the sky, the objects are rendered with the sun and moon rendered before the stars. This will cause stars to appear in front of the sun and moon, if a sun and moon texture is larger than usual.

It would make more sense if the stars are rendered before the sun and moon because they are farther away from the player.

Code analysis shows celestials are render in the order sun, moon, stars. A more logical order would be stars, sun, moon. (This would make no obvious difference with vanilla textures because the sun and moon are placed in gaps in the star field.)

To reproduce:
1. Enable the "Jupiter Moon" resource pack (it replaces the moon with Jupiter, also has a round sun)
2. Create any world (I used a void world)
3. Set time to 18000
4. Look up and inspect Jupiter -> stars are drawn on top of the "moon"