Probably other similar savers too.

$ vips colourspace k2.jpg x.v scrgb
$ vips copy x.v x.jpg 

Produces a black image.

VIPS_SAVEABLE_RGB_CMYK lets scRGB through, cast to uint8. Other savers need scRGB, so we can't just convert it. We should overhaul the SAVEABLE system, it's not very good.