Why am I getting a sensor warning even though I'm destroying it?

I am getting this warning all the time:

WARNING: sensor object went out of the scope but the sensor is still alive in the simulation: Actor 3447 (sensor.camera.rgb) 
WARNING: sensor object went out of the scope but the sensor is still alive in the simulation: Actor 3448 (sensor.camera.depth)

However, I am destroying it with:
destroyed:

all_actors = [camera['rgb'], camera['depth']] + vehicles
destroyed = client.apply_batch_sync([carla.command.DestroyActor(x) for x in all_actors])

The output of all_actors is as expected: [<carla.libcarla.ServerSideSensor object at 0x7fb5467139f0>, <carla.libcarla.ServerSideSensor object at 0x7fb546713090>, <carla.libcarla.Vehicle object at 0x7fb546713b10>, <carla.libcarla.Vehicle object at 0x7fb5467132d0>, <carla.libcarla.Veh
icle object at 0x7fb546713630>]

And there are no errors reported in destroyed.

What’s going on?

Ahhh, I see. I had to first call camera.stop() before destroying.