Vanilla install, reset world, non-admin user.
1) Create two fleet members (each with: core, reactor, 2 thrusters). Send them somewhere, wait long enough for the destination sector to unload.
2) Relog
3) Fleet still in place, members no longer in the fleet. Ships can be found via /search shipName
4) Find the ships, re-add them to the fleet
5) Relog
6) Fleet has no members again...ships found in space where I left them.
/search command was done via server console, logged-in player (Waldo) has never been an admin.