Other mistake: In each film Segal plays a chief petty officer, who happens to be an ex-Navy SEAL. In the posters for Under Siege, he's shown in the dress white uniform of an admiral. In the second film he's still depicted as an officer, but he has been demoted to a lieutenant. I guess the producers just thought the officer's uniform looks prettier, even though they're the very same uniform, except a chief has anchors on his collar and no shoulder boards.
Other mistake: When Commander Krill gains access to the captain's safe to retrieve the disc, the safe has no locks. (00:24:20)