I hate it when they do that... was the Tachibana cutting in front of the liner to come after your sub, after detecting you? The cause of the ships standing still afterwards is maybe from the damage the Tachibana suffered, and they were waiting on it to be repaired enough to continue, or they were waiting on it to prosecute an ASW attack upon thyself... I forget what the "hierarchy" of leader is, but generally speaking, the baton is passed to another ship in the group, and I am thinking it goes in spawn percentage order - but don't quote me on that...
Your image is from 0336 hours. What time was the liner "officially" listed as "Sunk"? Usually, within 30 minutes, if your submarine is not detected, they will continue onward. My guess, in the game, they stand still so that the escort has a better chance of hearing your boat. With seas like that though, it will be rather tough on them to find you...
