The HD color space operates without a setup. The downcovert most likely has setup added.
Remind your customers that HD and SD operate in different color spaces and the Kona, while converting from HD to SD does not ensure proper levels for SD outputs.
There should be two color correction passes done. One for each color space. The HD sequence can be duplicated and the Color correction can be tweaked for SD downcoversion while monitoring the SD downconvert. Also ensure that the monitor has been set up for the SD color space instead of the HD color space. If you do a proper monitor calibration in HD this does not mean the bars are correct in SD. The monitor needs to be re calibrated for the color space you are working in. This will affect HUE and Luminance vales.