I've noticed that when i had an scout on auto-explore and it got killed by an drengin ship the last known position of the scout had sensor sphere around it as if the ship was still there even tho the ship itself was long dead. This remained and persisted despite reloads and reboots and dozens of turns. This really kills the game for me as i can now see all the ship movement that the enemy makes on their way to my border and thus i can plan accordingly.