Strange ship behavior

Several times in a game I saw ships (not mine) that appeared to be attacking each other but they would for many many keep doing the same thing. What it looked like was the two ships where beside each other facing away from each other. Then the would both spin 180 degrees to face each other the move like to attack then spin 180 degrees apart then go back to where the started. No attack noises. This happened until a third ship came and killed those two.