Comment # 26 on bug 72685 from smoki

 Yes, as i see shadows are maded in gl_FragData but it touch GL_REPLACE
glStencilOp maybe that is because it show artifacts but not sure :).

 But comment is more about lockups in other bugs, where i see most lockups come
where GL_ZERO is used with glStencilOp/glStencilOpSeparate . I have The Cave
game which does not lockup when i just comment GL_ZERO op in state, the same
also with trace from Bug 64471 it does not lockup, etc.