This is true. Is the idea of your unique shader to use the same shader for every object?
Yes indeed,
While I understand the simplicity of that, it would result in alot of redundant calculations
Well, I was under the impression a if statement is a if statement... apparently, the portion inside a condition that is not being use has to be considered has if it was in order for the shader to render correctly. Strangely, the bug is not constant and very hard to track. I did noticed however that it rendered correctly when removing few objects from my scene which use no textures. I must be missing something.
...digging the uber shader.