Well, that is exactly the case I was thinking of. But stripping the metadata also should guarantee an image is imported as plain sRGB, which (eg. in GIMP) often may work out to no transformation at all.
I’m basically just doing the standard debugging thing – eliminate possibilities.
I put your case down to version differences. Since I don’t completely understand the bug yet, I’m just working on what I can.
… That’s not different in a practical sense. If you aren’t using available CMS metadata to manage the image, then there is no guarantee that your pixelwise operations on the image will make any sense.
In any case, my tests were designed to eliminate the possibility that Inkscape was correctly color-managing the image based on wrongly set colorspace information, which AFAICS they did. It’s pretty likely IMO that color management is unrelated to this bug (but at the same time, it’s the only guess I have at what could cause it.)
In other words, I am fairly confident that my theory is wrong. But it’s still the only theory I have so far 