Shader pass called twice?

I have a world-space UI canvas which is rendered into a render texture.
For some reason every shader pass of each mesh is called twice.

If the shader has more than one pass all passes are called twice one by one, e.g. #0 #0 #1 #1

Any idea why is this even happening and how to stop it?

UPD. Just forgot to mention that everything is fine in the Editor and this behaviour appears on iOS device (didn't check builds for other platforms though)

 

I noticed that this is happening by accident. I was implementing various blend modes and it appeared that "Multiply" is much darker than it should be. So I opened frame debugger and get surprised by what was happening.
So this not only affects the performance due to doubled draw calls but also breaks my effects since they don't look as expected.
I had a remote chance that maybe it's due to culling set to "Off". I thought that maybe Unity for some reason draws the mesh twice with back face and front face culling. But it isn't the case.

 

Thanks for reaching me out so fast.
It draws exactly the same mesh.

 

Hehe, well, I went through the captured GPU frame in XCode and surprisingly it shown that everything is fine and rendered once as it should.
Then I came back to Unity Frame Debugger and tried other textures (the white one as background, stronger contrast for the front one) to see the details better. And it appeared that it's just an issue of the Frame Debugger. It indeed makes the renderer draw everything twice as I described in the first post. But when it's disabled everything is fine.
What a relief.

I'll try to find some time to commit a bug report.