I logged in to find that one of my moons had been destroyed by a player who had moved insystem to me, and my fleet was returning from a colony mission. I had only just woken up so I was waiting for the inevitable flashing red triangle as my fleet was visible and I had no way to escape, but when the minutes went by without any attack happening, I looked more closely and my fleet was returning to M.O.O.N.S in slot 16. I assumed that I was still going to lose my fleet and that this was a new feature of one of the classes, but it returned to the planet as it should do after a moon kill. I asked the attacker why he'd not attacked me and it turned out that he could not see my fleet on phalanx, so for some reason it was not visible to him.
I think it is important to post this here because the attacker went to a fair bit of trouble and he should have got my fleet, but I escaped and I think all you fleeters need to know that if you kill a moon and do not see a fleet, it might not be because you missed it, but because some bug happened and the defender got lucky and escaped.