Exactly as the title says. Simply loading up the 3D editor placing a comment down with nothing else on the map will force a CUP addon dependency, specifically "Desert", even on Altis/Stratis/Malden 2035 etc. I've confirmed it only happens when CUP Terrains - MAPS is loaded and loading CUP Terrains - Core is not necessary.
Here's the simplest possible test mission demonstrating this behavior. It only has a comment in it. Simply delete the comment and then save the mission and notice how the "Desert" addon is removed from the mission.sqm