Despawn events missed when using FixedUpdate

[IVSOP]

I followed the custom setup example, but I used FixedUpdate instead of PostUpdate.
I noticed that, sometimes, the bodies/colliders of despawned entities would remain active in the world, when they should have been removed.
After looking into the plugin's setup code, I found

// These *must* be in the main schedule currently so that they do not miss events.
// See test `test_sync_removal` for an example of this.
if self.schedule != PostUpdate.intern() {
    app.add_systems(
        PostUpdate,
        (systems::sync_removals,).before(TransformSystem::TransformPropagate),
    );
}

So, despite using with_default_system_setup(false), self.schedule is still PostUpdate, which means this will not be called and sync_removals will not be placed in the correct schedule. In the example I mentioned, the custom schedule used is PostUpdate, so this issue does not happen.
To fix this, I used with_default_system_setup(false).in_schedule(FixedUpdate), but this feels like a hack since I will still have to register the systems again later.
My use case was I wanted to be able to pause the simulation, so I needed to add the systems and only make them run if the game is in a certain state:

        .configure_sets(
            FixedUpdate,
            (
                PhysicsSet::SyncBackend,
                PhysicsSet::StepSimulation,
                PhysicsSet::Writeback,
            )
                .chain()
                .before(TransformSystem::TransformPropagate),
        )
        .add_systems(
            FixedUpdate,
            (
                RapierPhysicsPlugin::<NoUserData>::get_systems(PhysicsSet::SyncBackend)
                    .in_set(PhysicsSet::SyncBackend),
                RapierPhysicsPlugin::<NoUserData>::get_systems(PhysicsSet::StepSimulation)
                    .in_set(PhysicsSet::StepSimulation),
                RapierPhysicsPlugin::<NoUserData>::get_systems(PhysicsSet::Writeback)
                    .in_set(PhysicsSet::Writeback),
            )
            .run_if(in_state(GameState::Running)) // only run if game is running
        )