I never used the map designer much in Trinity, so this may be something I'm just not aware of...
Every time I try to create a map, it inserts a random extra star (that doesn't show up in the star list) that has a single rebel-occupied planet. For instance, if I define two stars and their planet groups and planets, when I preview or play the map, there are three stars - two are laid out as I defined, and the third has that single occupied planet.
