Yep, the more I think about it, I believe you’re experiencing the default behavior of LIttleCMS with regard to applying rendering intents to a transform. I’ve done just this, I took a matrix sRGB profile and applied it with first relative_colorimetric, then with perceptual, to an exported TIFF, and they both came out looking the same. Later, when I put in rendering intent checking prior to the actual transform in my code, I got a “unsupported rendering intent” for the matrix sRGB/perceptual combination. And, the LittleCMS docs explicitly say that, if an unsupported rendering intent is provided to a transform, the transform will default to a rendering intent supported by the profile.
You can find a LUT sRGB profile here: http://color.org/srgbprofiles.xalter
And then, reading this might help: ICC Profile Conversion Intents One can spend hours at Elle’s ninedegreesbelow.com site, learning about this stuff, ask me how I know… 