Can be multiple reasons , but the fact is this goes for every kind of profile exchange.
Imagine you want to print to something that has a narrow gamut , but you have a monitor that is close to adobergb.
What you see is something quite different to what will happen when you want to export to print. There is no way to preview (softproof) what filmic will do with its gamut mapping when you export . What you see if way less gamut mapping applied compared to when you are exporting , with no way to control that.
The only way to do it properly would be to always export in your display profile , because that is exporting what you are seeing .
So if i want to export linear rec2020 , or someone wants to export to some other profile … It doesn’t matter. It still wrong you can’t control what will happen.
For me , I’d like to export a) in linear space b) in whatever the working profile is. To skip a conversion step , to further process it in next tools.
Anyway, when I export to rec2020 , and convert the result to sRGB , i get bright red with clipping.
If I’d see this in Darktable , i know i have to compress the gamut or try something with saturation.
But instead i see something purple without issue… Until i export.
Normally this is where softproofing comes in. If i softproof to linear rec2020 , you get that conversion in the preview pipe . It goes from working spaces , to simulated export space (still rec2020 in this case ) to display space .
The weirdest thing about it that the hue seems to shift , although i still have to check this with color pickers if that’s possible .