My camera with rendertexture still renders to screen.

Basic
I need render Spine object onto NGUI.
So I using RenderTexture and another camera for rendering. (Full screen size RenderTexture and a RenderTexture has many spine objects)
And I had link it's renderTexture to NGUITexture to render it on mainCamera.
I'll call them SpineRenderStage that is set of camera and contains spine objects.
I have many(about 4~5) SpineRenderStage instances from a prefab because every spine objects needs difference Ngui depth.
And Every SpineRenderStages's z position is enough to far so their area not duplicated.

Problem
At first, the SpineRenderStage's camera depth was 10.
And my maincamera (in UIRoot)'s depths was 0.
SpineRenderStage's camera is higher than mainCamera, but Every SpineRenderStage has it's renderTexture, so It don't render to mainscreen.
But sometimes it ignores and Rendered on screen and it appears higher than maincamera.
So I fixed camera of SpineRenderStage's depth to 0 and maincamera's depth to 2.
But It still happen.
Someone help me.

More Info
MainCamera is orthogonatic, and size is 1. (range is -10 to 10)
SpineRenderStage is two type, orthogonatic is size 1 and range is (-1 to 1) and perspective is 60 fov and range is (0 to 1).
every SpineRenderStage's x,y are same as MainCamera but only their z position are different.