EffectComposer overwrites previously rendered scenes

[JosephClay]

Passing a scene and camera to EffectComposer should contain the effects to the scene, however, rendering in this way clears previously rendered scenes (even with autoClear={ false })

Barebones test here: https://codesandbox.io/s/tender-galois-g55xlj?file=/src/index.jsx

[JosephClay]

I've tried several variations of the above in different forks without success

Just trying to run per-scene EffectComposers with a manually-managed render loop