Funny enough I made the same mistake in the D3D9 implementation of tex2Dfetch. Which is why it "worked", when it should not have. It's fixed now: github.com/crosire/reshade/commit/e1ae7c...282b6d7319d307eab464.
The OpenGL implementation is hard to fix. It needs to flip the Y coordinate, but that's only trivial if the input coordinates are guaranteed to go all the way from 0 to texture height. Which is not the case with your shader. Which is why it fails. Can't think of a good way to fix this unfortunately.
Cheers, crosire =)
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