Alright, I tried to reproduce as best I could.
Using just Galacticraft 176 and Optifine, on creative, I could not do it.
Using 175 and Optifine I could not do it.
Tried with and without my resource pack.
So, I decided to add Optifine back into the mix on my current game, and return to the moon - sure enough, it happened again (after a quit and restart on the moon).
Tried some crazy things (after a backup) - removed all mods besides those - no luck. Tried replacing the Galacticraft mods with the updated ones too.
I don't know, maybe it's save specific, or it's another mod that's creating a combination effect - I've noticed a few weird happenings on Mars that should not be.
For example - using the cryo chamber, does change night into day, but the day/night cycle is somehow not affected - what I mean is, even though graphically I see day time, mobs and solar panels are unchanged - I'll see zombies etc. walking around at day, and dying at night lol. Also, solar panels will not see the sun above them, but will be pointed at the ground at night and generating energy... I've found that quitting to main menu and resuming fixes this. Also sometimes turning the panels around 360 degrees with a wrench works too (usually).
And I get another bug that should already be fixed as well - using launch controllers between planets, the sound of the rocket continues well after landing. I'm betting it's likely another mod I've used that's messing with this. Also, unsure if it's supposed to happen or not, but when getting out of a tier 2 rocket on the overworld, I get fall damage
I am using DrZhark's Mo' Creatures mod - but when I first arrived at the moon, I found no mobs... turns out it was the Custom Spawner - which I uninstalled (with adjusting the flag/restarting a couple times as instructed), but I continued the same game - maybe that messed something up.
Also, this game was played LAN for a bit, and while I uninstalled it, my gf did not right away... so yeah, the save file is probably messed. I was thinking of starting over anyway.
All the other mods I have I could live without as well.... DaVinci's Vessels (and moving world) is useful for gathering livestock, but other than that I don't use it.
Just Enough Items and JourneyMap I could live without easily, but they're just convenient.
I do use Xray (I think it's advanced xray), but that's just for finding ores really so I don't spend more time mining than I have to lol. It was a little buggy though - it did not like the different tin ores on the overworld, moon, and mars - and I had to re-add them each time (although the color I picked was saved); and I had to restart minecraft totally to get the new ore to show.
Sorry for the long answer, but since you gave such a quick reply, I figured that meant you were interested.
I figure the more details I give, the more you may have an idea on what the issue is - and maybe you have an idea of what other mod I used that might have caused this (or even if it was LAN related, idk). If you have any ideas, questions, etc. please let me know - I'll see if I can try again perhaps. Maybe I'll just do an actual game with Galacticraft 176 and Optifine (not creative), and see if it happens. I didn't actually build anything on my quick tests today (just enough to get me to the moon) - so I could give that a go too.