Yes, I can reproduce it with a small litte test program that just loads a level and declares those skycubes.

I took a "normal" skymap and used photoshop to change its size to 6144x1024.
Then I made a copy of this skymap and declared them both as shown above.

After that the nexus is overridden.

[code]
ENTITY* cube = {
type="a+6.tga";
layer=2;
z=5;
flags2 = SKY | CUBE;
}

ENTITY* cube_moon = {
type="b+6.tga";
layer=2;
z=5;
flags2 = SKY | CUBE;
}



void main() {

level_load("telescope_room.wmb");

while(1) {
wait(1);
}

}

{/code]