The moon, the sun, and the Minecraft world form a straight line to one another. For instance, when the sun is directly above the player, the moon is directly below the player. Since the moon has phases, the illuminated portion of the moon is incorrect because the moon is in the incorrect position. For an explanation for the moon phases, see 800px-Moon_phases_en.jpg, which comes from Wikipedia.

What I expected to happen was...:
The moon should be at the correct relative position to the Sun and the Minecraft world for a phase.

What actually happened was...:
The moon stayed behind the earth, making the moon's position incorrect.

Steps to Reproduce:
1. Set the time to night. Any night will do except on nights that have a full moon.
2. Fly until you're able to see the sun and the moon from the same spot.
3. Observe that the moon is in the incorrect position.

The other 2 pictures show the most profound example of the bug. The moon should be in front of the Minecraft world, not behind it. Note: the Moon is in the same position as it were for a full moon.