Well, i also do not have planet textures in the map Editor but i thought this was intended... as soon as i zoom in up to a certain point ships & asteroids & resources do get to have some kinky graphics added but the planets simply tilt a bit left while two circles snap away.
Moon & rings only receive a general common texture, btw.
And, since we can't edit the texture files for any of these, i understood that SD coders wouldn't try to add this option in.
Thus, i don't think it is a flaw on you local system, ansury... most probably an in_transit_memory_slapping of available GDI calls which swap *indirectly* into the map Editor.
Although, is it that much important to have a (or many) texture onto each of these planets while you edit a map for later playing - as a custom map, needs not to be exactly random too.
I don't see an edit field to tag a texture file to any planets in the current interface though - not saying that SD shouldn't at least give us that sort of feature besides, teasing us with a terrific Moon tilt spectacular trajectories -- but, we can't experience THAT much in the game itself either.
And, thirdly why have a tilt for Rings when they simply always remain on the ecliptic whatever values we put in, or even resize INSIDE some planets while on tiny maps or somethin'?
So many things to "fix". CustomPlanets.xml(s) & StarTypes should load straight into that thingy, for one. Maximum sizes (I've seen PQ35's in some games!), some location restrictions (immense is supposed to be immense, isn't it?), backdrop nebulae alternative... so many more. A map is a fundamental work and it should NOT OVERWRITE some of the values every time, once we resave another round or just simply edited some key items manually only to have it replaced by defaults.
Foremost, i really want a spreadsheet context (cuts micman by 95% right there) before & more than any texture on these planets, though; i'd see these while i get to play, anyway -- unless customized for a reason or two, if that's what i want.