if it not via phase stabilizer or between stars everything should use the phase lane.

guess its a glitch.  only thing like i have seen is when two planets are really close to each other and slightly off the same plane.  ai ships kinda freak out close the edge of the grav well for a while and then finally jump or i get to the planet can kill them.  i kill them all dead.

i just hate it when fleets randomly fly off into the wide blue yonder on sub-light engines... it once took me 2 hours to get one of my fleets back into the grav well, because i had spent that time doing research and upgrades, rather that attack, so the fleet decided to desert... losers....

but its annoying, i wish the devs would fix that...