This is fine from a pure game mechanics point of view and only impacts the GUI.
At the start of the Settle phase, two objectives can be validated by the blue player (System Diversity and Greatest Military) for a total of 8 VP as long as he plays Alien Robot Scout Ship during the phase.
During the first part of the Settle phase, his red opponent completes System Diversity by playing a Novelty world. Blue plays a totally irrelevant card that doesn't complete anything. Since the phase is not yet over, System Diversity is not yet given to Red and can still be grabbed by Blue as long as he plays Alien Robot Scout Ship.
However, the mouseover pop-up shows it's not available anymore.
This is fine from a pure game mechanics point of view and only impacts the GUI.
At the start of the Settle phase, two objectives can be validated by the blue player (System Diversity and Greatest Military) for a total of 8 VP as long as he plays Alien Robot Scout Ship during the phase. During the first part of the Settle phase, his red opponent completes System Diversity by playing a Novelty world. Blue plays a totally irrelevant card that doesn't complete anything. Since the phase is not yet over, System Diversity is not yet given to Red and can still be grabbed by Blue as long as he plays Alien Robot Scout Ship. However, the mouseover pop-up shows it's not available anymore.