Circling Missile Bug
A known problem sometimes encountered with guided projectiles (those who have an ROT of greater than 0) is that when fired at a target, such a projectile will sometimes not fly into the target, but rather circle over the position of their target. Such a circling projectile may carry on to circle indefinitely, but it can also detonate spontaneously or when its target is destroyed by other means. Detonation upon destruction of the target is otherwise universally observed for guided projectiles (or so I think), but is not true sometimes for circling projectiles, which sometimes outlive their targets by extended periods of time, detonating spontaneously at a later time, or not at all until the session is ended. A circling missile will not follow its target if it moves, but will circle above the position the target had when the missile was incoming.
It is not known what causes this behaviour - it might be related to a low ROT setting on the projectile or a last-minute removal (by escape or destruction) of the projectile's target, just as the target is about to hit it, or it may be related to some other tags yet unexplored in this respect.