Brigo flyby/orbit/landing missions dont dissapear

This potentially might not be a bug, but it makes little sense and severely breaks the balance of the game. After obtaining the flyby mission and completing it, I obtain the orbit mission. I complete that as well as the fly by mission once again, and I obtain the landing mission. I do the landing mission, completing flyby and orbit again for a total gain of about a billion dollars, able to repeat over and over. So far in this game Ive spent about 3 million.