For example color(display-p3 0 1.5 0) is color(rec2020 0.7082 1.528 0.1721) and this ,correctly,gets gamut mapped because Rec BT.2020 is an SDR colorspace.

But color(rec2100-linear 0.5039 2.389 0.0447) should not be gamut mapped, it is an HDR space where (1 1 1) is SDR white and HDR colors have one or more components above 1.

I suspect this is because rec2100-linear is inheriting too much from the implementation of rec2020-linear.