some of the ships you get in the campaign have modules that reduce the logistics cost by 50%. i.e. the medium ships with that mod cost 2.5 instead of 5, the large ships cost 3.5 instead of 7 and the huge ship costs 4.5 instead of 9 (i think - not sure if the base cost for huge is 9 or 10). if you add up the numbers manually, the fleet probably has 25.5 points so you can't add +1 without getting over the cap of 26.

so it's more of a display issue, but it only affects the campaign since that special module doesn't exist outside of the campaign missions.