You're right. When you go over the Galaxy view and click on number 16 and have the following parameters:
https://steemnova.intinte.org/game.php?page=fleetTable&galaxy=1&system=132&planettype=16&planettype=1&target_mission=15
in the url, the button is chosen directly as it should be.
But if you're just going over your fleet to the expedition, that's exactly the mistake I've been describing.
Nice research! That info would be useful to fix the issue.