Noise Reduction: luminance +100 produces artefacts on non-raws

Hello, I noticed the following in the noise reduction tool. When setting the luminance slider to +100 (and all other sliders at default), the preview and the saved file show artefacts with non-raw files. More pronounced with 16-bit tiffs, less with jpg’s (but still there). Conservative/agressive or RGB/Lab doesn’t change anything. This effect isn’t visible with raw files.

16-bit tiff: