When I set a fleet to guard location and then had it phase from that location to another system, the fleet then started to cross space slow speed back to the previous location when an enemy ship showed up there, they were way outside the gravwell, about 2 diameters back towards the planet they had just come from and heading back that way. I could only stop them by changing the aggression stance and then they responded, prior to that they did not, & I replicated it.