GIMP changes R-channel, when it should not
Opening a new issue as I did not find an issue for this discussion https://discuss.pixls.us/t/gimp-changes-r-channel-when-it-should-not/8272
According to my findings the above mentioned change is caused by the fact that GIMP treats TIFF missing the tag TIFFTAG_EXTRASAMPLES as having the alpha premultiplied, other programs apparently treat them as with unpremultiplied alpha.
Adding a 0 to initialize also
fillorder causes GIMP to import the file as "RGBA u16" which in turns does not truncate/change R, G, B values greater than A.
I believe, but I did not check, that that image leading to that discussion has only R values greater than the corresponding A value.