The moon texture clips with skydome geometry, regardless of what the sky detail is set to in graphics preferences. If the sun is given the same texture, it does not clip.

Steps to reproduce:

1) Inventory->new settings->new sky. Edit the new sky.

1b) optional: set cloud density and coverage to maximum to see it easier, but it is noticeable as long as there are any clouds at all.

2) Move the sun and moon to the same azimuth and nearby elevations, I used 270 azimuth and 33 elevation for testing. The effect is worse at higher elevations.

3) Set the sun and moon to the same texture, for instance "moon" from the library.

4) Set sun scale to 10, moon scale to minimum. Move the camera around while viewing the sun; it does not flicker.

5) Set the moon scale to 10, sun scale to minimum, do the above; the moon flickers and clips against the skydome geometry. Changing the sky detail level in preferences changes the granularity of the flicker, but doesn't avoid it.

In the attached screenshot, top is the sun, bottom is the moon, moon has been set to 0 brightness. Elevations 45 and 30 respectively.