Canvas won't clear when using three.js EffectComposer

[brunoimbrizi]

THREE.js Example (http://soulwire.github.io/sketch.js/examples/three.html) normal render vs. THREE.EffectComposer render:
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Here is a working example: http://brunoimbrizi.com/_temp/sketchjs_issue/sketch.htm
Press T on the keyboard to toggle the effect.

When it is only three.js it works fine: http://brunoimbrizi.com/_temp/sketchjs_issue/three.htm