When specifying the Default flag on a [WorldSystemFilter] the flag will be removed and expand to what was specified as ChildDefaultFilterFlags by the group the system is in. This means the Default flag will never be set when querying a system for its flags. If the system does not have a [UpdateInGroup] the system will be in the SimulationSystemGroup and get the ChildDefaultFilterFlags from that group. When creating a world - or calling GetSystems directly - default expands to LocalSimulation | Presentation to create a standard single player world.