Sample average is slightly wrong if babl transforms are enabled, more wrong if not
Here's a compressed tiff in the linear gamma Rec.2020 color space, with "color blocks" for the Rec.2020 primaries and secondaries. The problem is in the tiff before I compressed it to allow not uploading a 1.6MB file, so please don't think the fact that I mentioned "compressed" means it's relevant to the problem. It's not, but I hope compressing the file didn't create any new problems.
rec2020-linear-swatches-compressed.tif
When color picking using Sample Average when the babl tranforms are enabled, colors are slightly wrong as shown by this screenshot:
When color picking using Sample Average when the babl transforms are disabled, colors are more wrong (look at the blue channel for the yellow block):
The yellow channel isn't the worst. For example try the green block when not using the babl transforms.
In my GIMP-CCE, all the color channels for all the color blocks read either 0.000000 or 1.000000, as they should.