LCh blend modes give incorrect results in color spaces other than built-in sRGB
As of babl/GEGL/GIMP-2.99 updated through this morning, the LCh blend modes in color spaces other than built-in sRGB produce wrong results. Edit: also using one of my ICC profiles from disk that match the built-in GIMP ICC profiles produces correct results.
For linear Rec.2020 blending a top layer with LCh=(50,50,180) over white using Lightness or Luminance blend mode produces L=51.1. For linear AdobeRGB1998, the Lightness and Luminance blend modes for the top layer produce L=52.4.
These wrong results are not dependant on whether the precision is kept at linear or non-linear, and survive the images being flattened and exported to disk and reopened.
The odd thing is that the Pointer shows the correct L values, only the color picker and the sample point dialogs show the wrong results. Except after flattening/exporting/reopening all three tools show the wrong result.