mrdoob/three.js — pull request #2645 by Janpotoms (2012-11-17 19:28:05+00:00)
Title: Actually clear the stencil

It seems like you want to clear the stencil here but you never make the call to `clear`.
I ran into problems with this in a project of mine where I based some of my code on this MaskPass.
important! I didn't test this, just wanted to let you know.